The worrying thing for me about rolling for stats being the default is that the rest of the game has to be balanced against something (monsters etc) so the base systems are going to have to take into account that characters are going to have wildly differing stats.
Well rolling for stats has been in D&D since day one! So I don't quite understand the beef about it. You can always use the other options, but really D&D isn't a point-buy system. And all they can do is give it their best shot at balance. As we saw in 3.X, it was like chasing your own tail and everyone has their own opinion about it. Not to mention sometimes its just not obvious even during play testing that something is out of whack; happens a lot with software.
This means 1 of 2 things - either the differences in stats are not going to be that important (in which case why bother?) or encounter and monster design is going to be a lot looser or difficult for DMs. I can see published adventures being very difficult to design well (or have to include lots of variance in encoutner setups etc).
Probably neither. Stats will be important; that is really one of the cornerstones of D&D. And really I think people overstate the importance of both encounter and monster design. The latter matters little, if the monster ends up being tough, well too bad, gain a few levels before you go after it. And for encounters, well, the DM can always fudge things if he's feeling nice and the encounter is too hard or such.
What is also worrying me is that the standard responce to people not liking a particular thing is "don't worry, there will be a module for that".
Well, to some extent, that *is* the stated goal of the 5e design. No matter how much the the designers and developers try, 5e won't be for everyone. If they try that, it will just be a losing battle for them. IMO if they get the core essence of both 1e-3e and 4e (just because 1e/2e have far more in common with 3e and 4e is just its own animal) plus add some new twists of their own, then it may just succeed.
And yes, like everyone else, if someone doesn't like a particular piece, or feels that X, which wasn't included, must absolutely be in the game, there is always "rule zero" aka house rules!