Me, I'm one of those people that hates change and complain when it's impending--then when I see it, I agree it's better than ever.
So, possible alternate settings:
I had a 4th ed saga starting in 1132 that used the backdrop of the succession war between King Stephen and Empress Maude in the Stonehenge Tribunal. It took heavy inspiration from the Brother Cadfael series.
My feelings about alternate settings are a bit mixed. I've enjoyed AM for quite some time and I think 5e is magnificent. But, authors need income, and a new edition looms. So an alternate setting might be a good idea for future editions: 5e pretty much got things right, IMO--a radical new setting would intrigue the people who want something new, but still leave us a very solid base for traditional.
I hate Steampunk as a genre. I vastly prefer fantasy. That having been said--is there thought of moving Ars MAgica to the Industrial Age? It's certainly a radical shift. I myself wouldn't be overly enthused about it, but I'd imagine many would. It does have fascinating possibilities and implications.
I had a few disconnected thoughts yesterday while trying to fall asleep. They may be a bit scattered, but hopefully they can provoke inspiration in others.
I liked how 5th ed gave each house a specific free minor virtue. I also think making each house a Mystery Cult, Society, or True Lineage was a good step. My main issue is that these are, for the most part, two groups: Those with a unique ability, and those who group to a particular interest. I find that the Mystery Houses are much more different from the other eight, than say Jerbiton is from Bonisagus. (Also, from a game balance perspective, each Mystery House gains something unattainable, while you can theoretically build ant of the other 8 houses identical to each other. Strictly from the numbers, you get a lot more options from Faerie Magic than you would from Puissant Singer).
Proposal: Give each house a unique minor virtue that is otherwise highly difficult to attain. This would require making 7 or 8 new mini-mysteries, so to speak. However, it does let each player take satisfaction in having something precious, unique about their character.
I've never been a fan of House Tytalus, but I'd be leery of removing a House altogether. (I'd also be very said to see Merinita, my favorite, disappear). Perhaps a revamping of some of the House philosophies does seem in order, though.
One major change I would like is the philosophy of adventuring. As it currently stands, magi in-universe generally are adventure averse. They get the most out of cooping themselves up in their labs for a season. I'd like to see better adventure rewards so that it's less contrived to send Magi out on a quest. Not sure what this would entail--perhaps being able to achieve adventure XP and still do a season's work? Or maybe allow 'mini-seasons'--journey for a month, but still be able to invent a simple level 5 spell if powerful enough.
I'd support ideas for possible higher fantasy and ways to interact such as summoning spells, slightly easier means of healing or convalescing, and so forth. Just a taste or two.