If there aren't any such complaints about the 4e->5e transition (and I haven't seen them thus far, certainly at nowhere near the intensity of the last time), then I worry. Unless 5e is so good that it sees a near-universal adoption by the player base (yeah, right...), then a lack of an Edition War is a really bad sign.
I'm not sure I agree with this. I mean, I hear what you're saying and see the logic of it, but don't think it follows that lack of outrage = lack of passion. It might mean
lack of passion about 4E. It could also mean, as you say, that 5E is good enough to please a lot of folks, or at least not offend them.
Its also a different cultural context. Whereas 4E "killed 3.5E and took its stuff," leaving it adrift without official support, 5E is coming out in a context that sees Pathfinder thriving, so you're going to have a large segment of players who will look at 5E and, if they don't absolutely love it, be content to remain with Pathfinder. In other words, people won't feel as burned - except for a relatively small group of 4E diehards who won't have the OGL for some entrepreneurial spirit to take the reins like Paizo did with 3.x.
I think the key, though, with 5E is whether it can find some way to interconnect the various editions, as the original intention was. The problem with distinctly different editions is the fracturing of the base into "edition factions." Couple that with the likelihood that the gaming population isn't increasing, and is probably even diminishing, then you have each new edition fighting over a decreasing pool of players with more and more options.
In some ways I'm reminded of the presidential election where there's about 40% of the voting population that will always vote Republican and about 40% that will always vote Democrat; the election is won by whoever gets the most of the remaining 20%. I don't know the numbers, but with regards to D&D players I'd imagine we have a few general groups:
Old Schoolers (playing editions pre-3E) that won't switch no matter what, except perhaps temporarily to try the latest OSR game - maybe 5-10% of the total D&D player base, perhaps less.
OGL/3.x/Pathfinder players - most of whom are happy where they are, and probably make up the largest chunk of D&D players - maybe 40-50%.
4E diehards - This is probably a relatively small group, but may prove to be stronger than previously realized. I imagine, though, that it makes up less than 20% of the D&D populace.
The Unaligned - These are the folks that are happy to try and play the newest version of D&D and/or are actively looking for something new, and/or didn't form an attachment to any specific edition. This, I think, is a solid number - maybe 20-30%.
Again, I have no idea what the actual numbers are. But the point is that 5E should serve two purposes: One, pleasing the Unaligned by making a game that is as fun as possible, that feels both fresh and classic. Two, trying to draw as many of the other three groups as possible, especially the 3.x and 4E players. I would guess that about half of each group would at least be willing to give Next a shot, but it may be that what would win one group over would actual disenfranchise the other, and it may be impossible to attract both (let alone the OSR crowd at the same time). But this seemed to be the original plan and it remains to be seen whether Mearls & Co can pull it off, or even if they're still trying to do so.
If Next is successful, my guess is that it vies with Pathfinder for king of the hill, with the 4E and OSR crowds being a distant 3rd and 4th place. I wouldn't be surprised to see the 4E diehards diminish to 5-10% of the D&D populace, perhaps not even that.