So Cam Banks asked in this thread "Who is Arm 6's Audience?" - and no one took him up on it.
https://forum.atlas-games.com/t/the-break-room/102/1
For a 6th edition, I think, honestly, a huge portion of the 5th edition audience as is. What I think many of us don't want is our 5th ed books completely useless. Yet at the same time, it's obvious from discussions here there are some of us (myself included) who would be excited to see the game turn a new direction. Whether this is a re-imagined Order of Hermes/Mercury with new house names & structure - to a more machiavellian/intrigue based OoH, it could be anything. I doubt any one group of fans would be able to agree on what direction to take the game. However, I think some kind of new direction and boldly committing to it is a good idea. However, What I think no one wants to see is Ars heavily split between 5th ed and 6th ed. Edition wars were not bad between 4e/5e, but I recall a lot more 3e/4e friction. Certainly no one wants to see something on the magnitude of the D&D 3.5 vs 4 vs Pathfinder split.
Also, from threads at other places like tgdmb.com. rpg.net, and other story game forums, there are a fair amount of niche/indie RPG collectors out there, who buy a core book, and maybe a supplement or two and move on. Never play, just buy, look over, and then later refer to it in other RPG conversations.
That said, I think making the game more accessible to new players is very important. I did have a guy in my group who thought he had to have his 4 players make 4 magi, 4 companions, 12 grogs and a covenant with the whole group before he could play. That is NOT how I have played it recently, but it was how I thought I had to start the game for about 10-12 years.
Style of RPG wise - what it seems Ars Magica players enjoy is a codified magic system, seasonal play, medieval/mythic Europe and being in a community of wizards. In current iterations, it seems also the target audience are players who enjoy at the very least a "medium" to "high" level of rules complexity and GMs who enjoy system mastery. I've heard this game being called "Logistics and Dragons" and there is something to that title.