The topic at hand is to analyze the effects of a combination of various Breakthroughs (and magitech improvements) becoming widespread across the Order. These include Subtle Opening, Fertility Ritual Magic, Wizard’s Initiation, Hermetic Ritual Initiation, and Fertile Longevity Ritual, as well as widespread knowledge of Principles Lore and effortless copying of books and quick travel. Which Virtues and Supernatural Abilities would be popular with magi and which would be deemed a waste of time? Wizard population may be expected to explode, but how much? Which social changes can be expected in the Order?
One likely topic would be increased need for vis and Magic auras from a growing number of magi. A more militant protection of vis sources and Magic places from mundane and Dominion encroachment is in the cards. Oath provisions to the contrary would have to be changed or ignored, but I expect the social pressure for it to be irresistible, Traditionalists be damned. However, it would be a stopgap solution at best. The only real solution seems further integration research to unlock means to increase supply of vis and Magic auras. This includes integration of Hermetic Alchemy, Hermetic Viresculture, Confluence of the Realms, Hermetic Architecture, and Mercurian aura creation and manipulation. Quite possibly a mix of the above is coming sooner rather than later as multiple researchers strive to provide a solution to the crisis.
Another likely issue is the inefficiency of training a booming apprentice population by means of the mentor-apprentice bond. Using a school-like system (hello, Hogwarts!) is the obvious solution. First to generalize its use for teaching everything but the Arts, incuding a suitable period of pre-Opening the Arts training, then to unlock a breakthrough to allow Teaching the Arts to multiple students. Again, I foresee no great difficulty for this change since the vast majority of mages can agree it is necessary and beneficial. At most, members of mystery houses and cults would ask to add a few provisions to the system to protect their secrets.
Of course, the Peripheral Code would need to be changed to prevent apprentice poaching by lawyering the Code.This involves recognizing a mage is fulfilling their requirement to train an apprentice properly even if they are not providing instruction personally. It also concerns protecting rights to apprentices that have not yet got their Arts Opened (including blood relatives of the mage), recognizing Opening contracts with InVi specialists, and sanctioning fosterage pacts. I expect no great difficulty about this reform.
As it concerns Supernatural Abilities being deemed valuable, I expect Second Sight and Comprehend Magic to be a worthwhile pursuit for almost any mage. Faerie Magic and Shapeshifting would also be good for everyone but the Bjornaer and the Jerbiton. Summoning (Spirit) and Chthonic Magic are going to be interesting for any mage that does not worry too much about Infernal taint, and Holy Magic for anyone that does not mind the behavioral restrictions. Divine Methods and Powers become easy to get for Holy Mages. The same applies as it concerns the other Goetic Arts and Infernal Methods and Powers for Infernalists. Principles Lore would be quite valuable for most mages as well. We may expect many of these Abilities to become part of the standard Hermetic curriculum, much as Concentration, Penetration, Parma Magica, Finesse, the Realm Lores, Latin, and Magic Theory.
Of course, getting full benefits from Faerie Magic and Chthonic Magic requires having the related Virtue, but I expect the lab benefits tied to the Abilities themselves to be available if you study them thanks to Subtle Opening. Probably the same standard applies to Holy Magic as well by analogy, but the rules seem more difficult to interpret in this case.
Widespread use of Principles Lore (or any other Lore equivalent without much of a thematic constraint, such as Children of Hermes Lore) effectively means self-Initiation for everyone in any Virtue they fancy. Existing Mystery Cults and Houses would likely strive to keep monopoly of their secrets, but theirs would be an uphill, losing battle. Criamon insights do seem self-protecting, but I wonder how much this would stay valid if you remove certain Ordeals from Initiation scripts. Which Virtues a mage would deem worthwhile of course heavily depends on their interests, but certain constants may be expected.
Virtues that improve learning of Arts and Abilities, extend life, boost various kinds of magic (let's assume prejudice against the Diedne is not a relevant issue in this scenario) and lab activities, remove Gift penalties, make the mage more attuned to the Realms, unlock new R/D/T, and/or provide new ways of using the Arts would be in all likelihood popular with almost everyone.
I am not sure which Supernatural Abilities from non-Hermetic traditions would be seen as good synergy with the Arts instead of a waste of time (and Xp sink). Maybe the Solomonic Arts? In most cases, integration rather than combining Traditions seems the way to go.
Of course, these breakthroughs pave the way for the average mage and their apprentice to pile up a lot of valuable Virtues and Supernatural Abilities without the constraints of a Mystery Cult or self-initiation. Hermetic Realm Initiation effectively means self-Initiation for everyone about everything, much the same as Principles Lore becoming widespread across the Order. The rules against having multiple Major Hermetic Virtues at character creation become even more constraining and dysfunctional (I loathe them, and have them removed in any saga of mine) than they already are. To balance things, adjustments to rules for teaching Hermetic Virtues to apprentices to make multiple Major Hermetic Virtues easier to have easier seem in order. Maybe a relevant breakthrough?