I'd be keen to see the Augustian antagonist. A Redcap would be my second choice.
If I had more time I'd offer to do a companion character, but I don't.
Since Magi of Hermes was released I've been toying with ideas to write magi for the Houses not represented in it. Like a Gifted magus Mercere, or a magus Trianoma (granted, House Bonisagus is represented, but only the researcher archetype not the politician).
I've thought about doing one or more of those for SubRosa.
Oh, but a Verditius could also be fun to design and evolve.
My idea for a magus Mercere is actually a half-way Verditius lab-rat who created devices for his House. Perhaps such two magi could work well together?
It is a concept I tried in actual play, to a certain degree. He wasn't designed very well for that, but a revised version of him might!
I'm game for a collaborative design activity.
Seconded.
There are a few advantages to doing cooperative work that I believe would make it worth the extra difficulty that it takes to coordinate different ideas.
Something that I did for Lambert, Ranulf, and Adelbert is to write up an enchanted device that they created in exchange for a different enchanted device which they could not have easily created. That would be the sort of thing that I'd like to do between the characters if we make multiple characters at the same time. (As in the instance where Ranulf has horrible vision and sucks at intellego so I had him trade a wand that creates light for a lesser enchanted device that casts eyes of the eagle. A few years later I was making Adelbert and realized that he had amazing skill with intellego, a restriction with complete darkness, and incompatible arts with Rego Ignem and Creo Ignem sO I decided that he was the other side of the trade and adjusted the eyes of the eagle device appropriately.)
I also see a harmonious justification to ignore certain capabilities if another of the characters excels at that thing. i.e. I normally feel bad about completely ignoring some field where magic is really applicable like communication, travel, or violence but if there is a related character that rules at travel or what have you then it is easier to justify neglecting it. Of course getting competitive about a particular ability could also be fun (Oh, yeah?, well I'm going to enchant a device that moves ten ships!! Take that!).
The third benefit I see in developing multiple characters together is magic that builds upon itself. One of the themes behind Ranulf was to create a character who rarely used just one spell when he could instead get the job done with three. I think that this reflects the way I actually see the game being played. "I already have a spell that creates walls of fire, I'll just create another spell that moves them/ makes them incapable of burning our wheat crop/ makes them as solid as stone/ reforms them into different shapes/ maintains them beyond the normal duration of the spell/ etcetera". With multiple characters involved it will be cool to possibly see spell combinations and interactions between multiple spell lists.
So how would collaboration work?
I like doing the core book mandated 30 xp per year of study. It makes the created characters kind of match what is in the published material. It eliminates discussions about how high quality sumae allow characters to accumulate skill faster than my personal tastes enjoy and it describes an order where taking seasons of exposure or adventure xp happens fairly frequently which allows us time for adding in descriptions of how time pass that allow for more than "spent two years in the library".
30 levels per year is a weird thing. I've always just written out the lab time season by season. This makes the characters I end up with differ from the ones in the published books where the author didn't do this a fair amount (the detailed development character ends up with far more spells and devices). I think that this more work intensive method makes more believable characters in that they do what they can. I once tried to recreate Timothy's Alexander from MoH and found that in the first 15 year period he developed a bunch of spells that were at the very limit of his lab totals (like inventing a level 30 spell when his lab total was 31) which is legal by the rules but hard to imagine how it was pulled off without lab notes for a spell that was very clearly Alexander's own. I guess I'd be happy to collaborate with someone who only wanted to do the 30 levels per year rather than write out each season of lab work, but I'd be even more happy to work with people who wanted to dig into the details with me.
I think that it would make sense to produce a character at a given time period then discuss with the others what they planned for the next 15 years to see how things can interact, Then after a bit of discussion and reworking of the material go on to the next time period.
I think multiple threads one for each character with lots of links between them rather than just one thread with multiple characters in it?
Does that all sound OK?
I'd like to participate in such a collaborative design process (I sent you a PM), and I'd like to use the detailed method. I think your suggested method sounds fine.
So we're talking about a couple of magi being designed and developed, with some degree of interaction? We should pick a Tribunal to integrate them into, perhaps? And choose Houses! I'd like to look at some of the Houses and archetypes "missing" from MoH. There are no magi Bjornaer, Guernicus, Mercere, Tremere. Of these missing Houses I think I find Mercere the most interesting and all in all the most under-represented House throughout published material.
While there is a Bonisagus it is a Researcher and a magus Trianoma could be interesting. Flambeau is well-represented but there are still Schools unrepresented. Ex Miscellanea is also a very diverse House and only one of the traditions from HoH:Soc is included.
I'd really like to see what someone could do with a Gifted Mercere. IIRC, there's no actually officially statted Mercere magus in ArM5 (there's only the basic template in the ArM5 corebook). We hinted at a few in the Provencal book but I don't think any of them were written up.
See my "More than Messengers" section of my blog for some commentary, links to relevant threads and also a listing of the canonical / deuterocanonical Redcaps and some worked through examples in a similar style (I've statted a the Redcaps Cymena and Sicart at 3 age levels, using my "Redcap Training Packages" rules).
I'd be interested to see what you guys get up to in any case - the lack of a Guernicus and Bjornaer needs to be rectified as well IMO.
You could start by having a look Sub Rosa - where there's a Guernicus and a Bjornear created and advanced in painful detail 
I believe that there is also a Guernicus in Antagonists also there is this one developed over 19 pages and many months and discussions that I'm rather fond of Adelbert, a "Magi of Hermes" look at intellego and Astrology. (although if I were to do him again I'd give more xp to the familiar)
I had a similar idea a few years back, so much so I named my blog "magi of Tom" as I would surely create magi to rival those in magi of Hermes. Sadly, it ended up a random collection of Ars bits and pieces, but I am proud of the Mercurian Guernicus I did.
So Erik...choose the theme, and then your would-be collaborators will bombard you with PMs.
BTW, I was looking at Vitkir - do they get 30xp/year like Hermetic magi, or should they spend a little time working? The one I'm generating has extra craft skills in case he needs a day job.
Personally, I would love to see an example Guernicus magus, since it is (I believe) the only house not represented in MoH.
MoH has no Guernicus as well as no magi Bjornaer, Mercere, or Tremere.
I'm sure there are magi Guernicii in published ArM books - I believe one of the Antagonists, as well as a young Quaesitor in Thrice-Told Tales in the Servants of God chapter. There might be others but this is off the top of my head.
Guardians of the Forest has Tabanus filius Jart.
I've just finished editing that article for issue 18. It's a great effort, actually. Very interesting to see the different ways they advance and how it plays out.
I did a Guernicus last time I did this exercise Adelbert, a "Magi of Hermes" look at intellego and Astrology
I'd really like to see what can be done with a vitkir, a Redcap, or a Gifted Mercere. 
Yep, a GIfted Mercere would be good to see. I advanced one of my Redcaps, an ArM5 version of Cymena of Rorschach, 22 and 43 years post Gauntlet. Beyond that her Longevity ritual became ineffective in story.
Without a longevity effect, a vitkir would be interesting.
A properly done detailed sahir would also be interesting.
I have plans for making a fully detailed Sahir, but I keep looping on myself with the idea 
I tried that once. I had a plan for a agricultural focused character who made his little corner of the desert into a lush paradise. Sort of a Sahir version of Gwidion. I found it very difficult to do requiring me to create a whole bunch of appropriate jinn, the sahir abilities themselves don't easily lend themselves to the task. I gave up very quickly.
I've experienced this problem as well.
So I've been trying to write a collection of Jinn, but that has turned out to somewhat larger undertaking.