Waiting for a new edition of Ars Magica could have you waiting for a long, long time.
As far as I know there are currently no plans for a new edition. That can of course change, but seems unlikely to happen in the near future, and even if it does it will take time to write this hypothetical new edition.
There is no reason to expect a new edition; we are a small community and the publisher does not find it easy to make a business. We keep hoping. Of course, the publisher may have something to add to this.
I suggest you just jump. Ars Magica is something different. The flexible magic system has been copied by a few other systems, but is still very inspiring. The semi-historical setting of Mythic Europe is IMO much more inspiring than pure fantasy settings, and I have not seen a similarly elaborate Mythic setting. The idea of the covenant (household) as the principal character, with characters developing long-term over decades or centuries is something I have not seen as well supported in other games, and it offers broader set of challenges. All in all, if you like these features, go for it. I don´t think you´ll find a substitute.
Beyond what has been listed above, a transition from 5th edition to 6th edition would require making some controversial decisions, which would both alter the nature of the game and drive some portion of the base to stick with 5th edition, so aside from it making an even smaller market it would mean if you do jump into 5th ed and there was a new edition, you would continue to have a large player base willing to stick with you.
The absolute best time to get into 5e is when Atlas Games do a bundle of holding, so you can get a stack of PDFs cheap.
Another good time would be in the next few days, so you have enough time to read the rules and get a vague handle on how characters work before the next Image from the wizard torn online convention - the wiki gives the dates of the initial one in November, but another one is organised for February 5th to 7th. If you get on with online roleplaying and want to play whatever weird and wonderful one-shot adventures people have, this is a good opportunity.
Reign, by Greg Stolze and the crew in Blades in the Dark are the only other games I’ve played where that collective central “character” thing seems to be well done though in both it seems a bit more narrative than in Ars.
While not as well done as AM, I have been in CP2020/Traveler games (Corporation) and Mechwarrior games (Merc Company) in which the central entity was not the player characters but the organization. Games like this have a different feel from character focused games, were the death of a character does not feel nearly as much of a determent to the overall game.
I enjoyed that game, but I found that the mechanical system for the houses was a bit disjointed with many of its interactions with the rest of the world. Also, the heraldry chart is alphabetically ordered, but the roll is like 7d6, meaning that you never get a heraldry that starts with early or late letters in the alphabet...
I agree 100%. Right now, I'm currently very excited for the Iberian Tribunal book (as I do speak Spanish) but I really wish there would be more books as well. Personally, I think a decently advertised Kickstarter would help gauge interest and viability. I heard there was an Ars Magica video game Kickstarter that didn't go through but, unfortunately, I didn't hear about it until after it was done. I definitely would have supported it if I knew about it.