Other things that I wish would be clarified/modified are:
0.) More inherent conflict in the setting. History we can't change, but a OoH that has more intrigue would be good. This could be the introduction of more rival magical orders, or a much more significantly disunited OoH as the base premise. I dunno, what if the OoH was actually an integration of rival roman orders that never liked each other much in the day, and that still causes problems?
1.) The power level of texts - many threads here have been devoted to the prevalence of high quality summae and tracti. Some propose chucking summae, and just using tracti.
2.) Muto - what definition of "unnatural" should be be used to adjudicate the level of a spell? See tgdmb.com/viewtopic.php?t=54753 for discussion on page 2 & 3 I think.
3.) Change the Houses - or at least some of the names. Jerbiton is the worst offender.
4.) Scribing rules - why does copying a Level 5 Summa that contains 50 xp, take the same time to copy as a Tractus, containing 10 xp? (Comm+Language levels per season, unless I'm mis-remembering).
5.)Muto Vim - I just don't even let my players use spells from this section.
6.) Muto Mentem is still weird
7.) Some arts, Auram, Auqam don't have nearly the utility of other Arts such as Corpus or Vim.
8.) All abilities/Arts using the same scale. I'm personally fine with two different scales, but for new players it seems to be a huge mind fuck.
9.) Lots of play testing just like 5th Edition received.
10.) More powerful base characters. My PCs start with 500xp or and they're still not that powerful because it's spread around.
11.) Support for different eras of play - i.e. "In the 700s, add 10 levels to the base level of all spells. Divide by 30 for longevity potions, the Art of Vim doesn't exist yet, instead do X etc."
12.) Clarify the Aegis of the Hearth - great spell idea, but some thread on here has a huge multipage list of how it works.
13.) Magic Resistance rule clean up
14.) Rebalance some virtues & flaws i.e. Short Lived Magic my troupe found to be worthy of a -3 flaw, not -1. Magical Foci are very powerful, Mercurian Magic is not a +3 virtue. (To my troupe!)
15.) Rethink the setting, given Mystery Cults and how mechanically, they lead PC groups to absurd optimization. Or be upfront that NPCs and PCs use different rule sets, and that's why the NPCs haven't changed the world yet.
16.) Much bigger set of virtues and flaws in the Core book.
17.) Bit more involved combat system - equally statted PCs vs NPCs are a HUGE grindfest depending on the circumstances.
18.) Hints of other Ancient Magical cults, i.e. Cult of Jupiter and possible descendants.
19.) Spell out the base paradigm of the setting in the corebook, if we're going to use Arts and Academe as a reference.