I won't speculate on the business wisdom of such an edition, but it sure would be nice to have one that combines TSR simplicity with WotC's unified d20 and 4e's focus on balance.
I don't think that a focus on "balance" would be a serious factor in getting non-4e players to buy 5e. Frankly, to an old-school player, balance is probably the
wrong thing that D&D should ever focus on.
I think the version that 4e was a turn-off to so many people who played one or more of the prior editions was due to (1) the powers system and (2) the idea that everything has to be balanced.
The first time I tried playing 4e, I looked at the cookie-cutter "every class does essentially the same thing but calls it something different, and they can do it # times/encounter/day" and thought "booorrrinnnggg!" I even shook my head at the "at-will" powers - if it is at-will, why isn't it just a normal class feature like in previous editions?
It is precisely
because each class, spell, etc. was different that people played the prior versions of the game and spent so much time customizing them. Besides the obvious ability to do so due to the OGL, there were far far more fan-created additions/modifications/changes to 3.x than to 4e. You could come here on ENWorld every day and there'd be a new feat, prestige class, conversion of a monster or module, or just plain new creative works. I don't see that at all with 4e - it feels like things stagnated about 1 year after 4e came out.
Another issue is that a game can be a lot of fun, regardless of which mechanics are used. For example, I'd love to see a conversion of the Twilight:2013 lifepath system and mechanics for use with D&D-type games. WotC could make a new version that uses a lifepath type of character generation system and still
feel like D&D in play. Essentially - WotC needs to be smarter in regards to which sacred cows they keep or ditch. Unfortunately, with 4e, their choices weren't all that smart.
No - I think that for a 5e to be successful, WotC wil need to do two things -
1. Make a great version of D&D that
feels like D&D and that is backwards compatible with 1e-3.x while raising the bar for things that have been previously neglected (like a character generation system that is more than just the numbers, and a way to modularize rules such that players can choose as much or as little complexity as they want). 4e doesn't feel like D&D.
2. Eat some crow and admit that they made a mistake with the direction they took for 4e. Relegate it to being a "spin-off" game and go back to basics.