What about formal wear?
Formal wear would probably not be magic. It would be like going to a diplomatic meeting armed, yes?
That's one point of view. Mine is that the world we have today is because of the activities of the Order. Verditius Technical Laboratories Incorporated, located in Italy. The Order created the United States (one of the early revolutionary slogans was "Join, or Die!", indicative of the Flameau influence). The Mercere invented the Internet (and use spells to magically travel along the wires).
And you don't? I do!
Going UNARMED to a diplomatic meeting? You must be crazy!
I mean if you do, then you cant defend yourself from that nasty threacherous counterpart when THEY come armed!
Or, variation:
What would be the point of going unarmed, thats when they wont be expecting you strike their perfidious hides down like the sheep to slaughter they are!
Nah... Not likely. And i would much rather play "openended", otherwise there´s a million and one events that must go down EXACTLY as it historically did, or the future changes completely.
Yes, so long as the Gift is an issue, you can't make assembly lines for the high end stuff. In the real world, hand made was better, but not that much better. The Ars Magica magi items are so much better that they will soak up all the money.
Don't limit yourself by thinking that.
Make some Unnatural Metal aka high grade steel made with tungsten, you know airplane wings.
Turn it into yarn. Weave it, let it turn back. Now you have a shirt stronger than anything known to man at that time.
Anyone with access to Islamic scientists, their books etc, would be able to do amazing things.
Except you don't. Items of Quality are known in the world, and they make a stronger shirt then is possible with metal, and you made it out of silk, so it's comfortable.
Airplane wings made in steel, wow that would be a novelty, for a very short while.
Aluminiumbased alloys or more recently carbon fiber based composites, that you might get airplane wings from.
BTW, you know what "tungsten" literally means in Swedish?
~"heavystone"
Now guess why. 
Add knowledge from China, India, Egypt, etc etc... Many cultures managed to excel with something.
And if you have a love for the possibility of ancient flying machines, you should have a look at the old Indian stories.
A mage can do much better. Make spiderwebthread and weave it equally mixed with unnaturally perfect quality silk over a titanium-aluminium metal base with a fairly thin titanium-tungsten-carbon sheet as the outermost hardshell layer...
That by the way is one thing that a history of mages would change radically, metalworking and what substances were put in use when, because magi would be able to both separate composite minerals into their individual parts(making aluminium production possible) as well as making it easily possible to work on such extremely difficult metals like titanium.
Hehe, the era of the heavy cavalry might just live on for a few hundred years more. 
I love people that know more than me 
I only mention Islamic scientists because of some of their scientific breakthroughs... Especially in optics and medicine. Mostly their approach to science more than what they had done at the time.
I didn't mean to hijack the thread 
I as far as clothing goes Dire, I agree a magus could definitely create better magical clothes. I meant that non magical clothing and armor could easily be made better with minimal amounts of magic used to alter the materials.
You didn't hijack the thread, it is supposed to be "Let's Pretend". As to your last point, the problem is that both magic clothes and magical improvement of clothes take someone with the Gift. Magic clothes are tremendously better, and improvement of clothes is just better. Given the limited time people with the Gift have, I just don't see option two happening.
What good is magic if it doesn't improve your life? 
Magic clothes takes at minimum a season for whatever effect you are putting in and requires Vis. For 1 pair. Improving the process of making better mundane items is trivial and cheap.
Imagine making a wand, unlimited charges that has some Rego Terrem effect to shape metal into a ring. A seriously easy effect to achieve. However pinching the rings closed was the hard part of making ring mail.
Yes, but this is the Middle Ages. If I have the skill, I will not make some cheap gimmick, I will make Art! Clothes that will be talked about hundreds of years later! As to ringmail, who cares how long it takes a grog to do something? Are you so heartless as to have him starve?
My point is a Grog can't do it... because the tools and the knowledge of smithing at the time prevents it.
There are definitely many other things you could make to help out the grogs. Like a Rego Aquam wand to separate pure water from sea water... The result Fish and sea salt in one reservoir and fresh water in another.. Very valuable.
Instead of Dredging by hand to evaporate water in the sun for sea salt, build a Dredging wand Rego Terrem effect. Then when the Grogs are done Muto Terrem solid rock to dirt, mix the dirt with clay, lay the foundation... Magic wears off... Cemented reservoir for when the tides come in. What that would take a Day of time? The wand 1 season...
No. Just NO! A thing like Kallistas suggested item for bending rings for ring mail? It would cut the time it takes to make a high quality mail at the very least in half, and by doing it reliably and identically every time it would be almost invaluable to an armorer.
Its the kind of "cheap gimmick" some people would literally start wars to posess.
"I will make Art!" is really a ridiculous claim that might be true for for one craftsman in a thousand. The rest would nearly beggar themselves to get such a "gimmick".
then make arty clothes!
There are no paradoxes. Whatever happens in your game world, hundreds of years later the worlds still winds up the way it is.
Mostly.
It is still a fictional world with fictional institutions and fictional history. In essence, the world turns out the way it does because of the random actions of player characters.
A million and one events do go down exactly as history records. Those you don't have to worry about. It is the one-hundred-and-one events that your game encompasses that create the differences between the real world and the game world.
Except when players just happens to make that impossible.
So they kill the king of France. Big deal. A different royal lineage takes over, during the revolution King Barney and Queen Betty are the ones that get executed instead.
A lot of stuff inbetween then and now may look vastlly different, but ther end results are amazingly similar.
For example, New Yourk only grows to half its RL size. But there are several additional eastern seaboard cities that pick up the slack. One is called Metropolis, another is Gotham city
And I am not so much referring to your own specific game world. Moreso, I am imagining that the world of ME, left to its own devices, could indeed still evolve into something resembling the modern world. A fictional and mythic modern world.