Wouldn't a Major Breakthrough Integrate "Gentle Gift" into Magic Theory, removing it's virtue status? I think you are being too harsh, for the effect. I would make it a minor breakthrough, with a note that another minor breakthrough would finish the integration.
A Major Breakthrough creates a new Hermetic Virtue which can then be taught (standard rules for teaching virtues applies). The Gentle Gift is already a Hermetic Virtue which can be taught (canonically speaking), as per Apprentices, and it can also be gained in certain mystery initiations.
IMO, it would be a Hermetic Breakthrough to make it so that all who have their Arts opened a certain way have the Gentle Gift.
The effect is substantial, in that it devalues the Gentle Gift virtue and also grogs and companions. Were I a player in a saga where this were developed, I'd be relatively honked off that someone with a pretty low Parma could do everything my character could do. Picking Gentle Gift is a huge sign to the SG saying, I want my character to participate in stories with mundanes and be reasonably certain I can succeed in those social interactions.
Thank you Mr. Link. My understanding was that you needed a Breakthrough to create a Hermetic Virtue that can be taught, and with another Breakthrough, you removed to need to "teach the virtue", effectively improving the understanding of Magic Theory for the whole Order, spreading to each magi as his MT went up. That was my understanding of "After the breakthrough", page 9 of Ancient Magic. The avowed "Parma Civile" would seem to be half way to that goal......
In some ways, this would seem to turn one's Parma inward, to prevent the effects of the Gift from escaping and affecting others. By this reasoning, would it be unreasonable for your Parma to affect all of your own castings as well?
I was thinking about that approach too, but wasn't sure how much of the lore aspects of what it might be doing should influence the mechanical game effect. Instead I started with the mechanics and just mentioned the effect that Parma Magica already has, which is to allow Magi to ignore each other's Gift. This is an extension of a concept already present in RAW.
Potentially Parma Civile could instead reduce the user's Parma to zero regardless of their level, although base art resistance should remain, and also apply a casting penalty to all spell casting attempts. Having the Parma score as the penalty makes sense from the view that the magus must cast through their own shield, but it does not reflect that a person with a higher score should know more about how to avoid their own parma too. Perhaps a high penalty which is lowered as skill increases; penalty of 10-parma, with a minimum of 5?
In terms of the difficulty of the breakthrough, all the other Parma mods are Major; and it is certainly not a Hermetic breakthrough, and certainly not minor. The discussion of comparison to the Gentle gift is interesting, remember that a major breakthough is likely to take decades of work, so granting the discovery akin to a +3 virtue for a decade of research is not unbalancing imho. That is very different if though if the discovery has now been spread throughout the Order. Perhaps a setting which has a Parma Civile concept should also reduce Gentle Gift back to a +1 Virtue, to reflect it's reduced mechanical influence.
That's pretty much the case - the clarification is that ANY virtue that is a Hermetic virtue can be (technically) taught, via the Apprentice rules - or if it's a Hermetic Ability, it can be taught normally, like a regular skill. Gentle Gift, as a hermetic Virtue (even though non-hermetics can know it), falls into this category.
The second integration, as you said, removes the need to teach it - it becomes integrated into Magic Theory (or into the Opening of the Ways ritual), and anyone who spends a season studying the relevant Tractus can learn the technique.
That being said, I would suggest that this fold, rather than being an incremental step towards Integrating Gentle Gift, is an alternate way of dealing with the same issue. You still have the gift - you're just figuring out how to shield against it more effectively. (VHS versus Betamax, basically - the end result is very similar, but they're based off of different principles.)