So - just noticed that bit of text in the Mercurean Temple entry in Mythic Places (pg 100):
So..a question on that. Mercurean Magic is already Hermetic - meaning that if the Integrator in question already had Mercuearn Magic, it would end up as a Full Integration. What would that look like? For most integrations, it's "Everyone gets the Hermetic Virtue without having to specifically learn it". But Mercurean Magic has a pretty large disadvantage associated with it. Does the inability to perform quick Spontaneous magic also get Integrated as well?
My initial thought is "no, it would only integrate the ritual use of Vis, and the Wizard's Communion ability" - but that's actually not how it usually works.
But if that's the case, then perhaps that explains why it hasn't been integrated already: druidic spontaneous magic really is irreconcilable with efficient roman ritualized cult magic. The Mercureans realized that not everyone would appreciate being unable to do spontaneous magic - and so they purposely kept it as a separate virtue. (Or alternately, they HAVE integrated it - they just keep the tractus out of general circulation, and their 'initiation' is "here, kid - read this.")
Without more of the text to read, it seems to imply that 'discover' means you're just re-inventing the virtue, in which case you're getting all the ups and downs of the virtue. Someone deliberately integrating it into Hermetic Theory would very probably deliberately be trying to remove the downsides, otherwise there would be little point, as magi probably value quick Spontaneous Magic over 1/2 vis use in rituals.
Oh, sure - that particular snippet is the last sentence in a call-out box. The text prior to it simply discusses the OTHER things you can integrate from the Mercurean rituals - how to punch a permanent hole in a Regio wall, etc. (Although it seems that the Mercurean rituals fall into that rare category of Sources in which you can gain more than one breakthrough from them: you can integrate their Ritual effects, or you can study them to Integrate Mercurean magic.)
And I do agree that if you don't have Mercurean magic to begin with, then you'd just end up with the Mercurean Magic virtue - however, for Major Hermetic breatkthroughs, that's the first step in Integration, regardless. (ie: step 1: figure out how to develop a Hermetic Virtue version of the ability.) For a Hermetic virtue that does not yet exist, that's normally done by studying Sources to get Breakthrough points; however, if the virtue already exists, you can probably just get it taught to you the normal way. (ie, through straight Instruction, or through Initiation.) The second step is gain the same number of Breakthrough points AGAIN (albeit from different sources), and thus fully integrate it into Hermetic theory.
However, as Mercurean magic has an inherint Flaw built in...what happens? I mean, every other Integration that I've seen only adds to Hermetic Theory - not taking away. And if an Integration 'breaks' something - it's usually done in the transition from "Non-hermetic ability" -> "Hermetic Virtue". For example, that prophecy ability in Rival Magics( or Hedge Magic - I forget) looses its ability to break the Limit of Time when it gets translated into Hermetic Theory. But in this case, the modifications would have to occur in the translation from Hermetic Virtue into fully-integrated feature. That's not how it seems to work in any other Integration; hence my question.
Now, it seems that this would be a simple thing to resolve: just don't use that part of Hermetic magic when you're casting spontaneous effects - I mean, you learn it from a tractus, rather than having it burnt into your head via an Initiation script. But this begs the question as to what it actually MEANS to Integrate. I mean, I can ignore a potential technique when I'm programming with a real-world language, or not use a certain set of vocabulary words when speaking an actual language...but I'm not sure if you could do that with a Hermetic breakthrough.
EDIT - although, in thinking about it a bit more - any non-hermetic ability that gets integrated as a Hermetic Ability runs into the same issue: the aforementioned prophetic ability, for example, gets integrated as Hermetic Divination. What happens in the next step of Integration? Does it become 'just' an ability that automatically becomes available whenever someone learns Magic Theory? Or does it become more fully integrated into the classic TeFo framework?
I think integrating something into proper Hermetic theory will strip the negatives out of it by default. Mercurians have a problem with spontaneous magic because the way they cast spells doesn't mesh well with regular hermetic magic. Integrating Mercurian Magic should correct that problem (and in fact, it's one potential GOAL of trying to integrate Mercurian Magic, rather than extending the benefits to other magi), allowing Mercurians to cast spontaneous spells normally AND allowing everyone else to cast rituals at 1/2 vis cost and getting free Wizard's Communions.
But look at other potential integrations (Hedge Magic, Ancient Magic, Rival Magic); often an integration does not produce a duplicate effect, but rather a similar effect in Hermetic terms. Integrating Mercurian Magic need not give everyone exactly Mercurian Magic, but something better suited to the broader Hermetic Theory.