A certain amount of the negative side of that is inevitable. But likewise, I doubt they will totally miss out, either. After all, people who post tend to be more vocal than those that out there playing. For every person potentially building a grudge here, there are many out there that just want a new version that has craft rules or rules for building a keep or whatever. You could satisfy a lot of them with add ons to 3E or 4E. So certainly a new edition that does even more will at least get them to pay attention.
So worse case in your scenario is that they only get the easy to get new customers, and not very firmly, either. You'll see a quicker drop in sales than you would with something more engaging, like a movie that isn't a complete stinker, but whose word of mouth hurts the followup weeks.
The real theoretical worse case is that the old D&Ders, 2E guys, 3E/3.5/PF guys, and 4E/Essential guys all get their points across, but the effort to try to accommodate all of them aims too high--and produces a mishmash that doesn't even objectively work, let alone please anyone. I'm not worried about that.
Best case either way is that WotC is smart enough to ferret out the useful informaton presented and make a solid game. And I've got better than usual hopes because of the "version 3.0" rule invented for Microsoft software. MS never gets it right until the third full version. (And most software companies suffer from this somewhat.) There are lots of complicated reasons why this has some merit, but mainly it is because it takes two full cycles "out in the wild" to really figure out what the heck the customers want and need. I see enough of the version 1 and 2 software mistakes in WotC's first two tries with D&D to think this might work for games, too.
On the negative side, that means skill challenges would not be perfected until 6E, and anything introduced totally new in 5E will start fully working in another decade or so. Fortunately, it isn't an ironclad rule, and wide playtesting is the main way you fight the problem.