what ever it is I just hope that one rule from the 3e and 3.5 book doesn't make it in... "Fighters can't have nice things". (and before you say it isn't in there, I promis you it is, just between the lines.)
Well, that's not strictly true and-- (looks at user name) Ah. Right. Well, carry on.
In addition to that, 3e was also a massive hit because it was a much needed renovation of D&D in multiple ways, but especially the rules set.
Which, in a nutshell, is WotC's current predicament. 3E was a hit because there was a large population of dissatisfied gamers. It succeeded by largely implementing a bunch of stuff that AD&D players had been house ruling into their own campaigns for years.
With 4E, it's fairly clear that WotC's designers thought there was a similar body of dissatisfaction. In retrospect, it appears they were led astray by the specialized echo chambers of CharOp and organized play. They introduced solutions a significant portion of their player base didn't like for problems a lot of them weren't having.
As a result, the player base split.
Is anyone seeing significant dissatisfaction in the 4E player base? The closest I've seen is dissatisfaction with the online tools and dissatisfaction with Essentials. Neither of those suggests to me that a significant majority of 4E players are consciously or unconsciously hankering for a new edition.
There's significant dissatisfaction, of course, from former WotC customers who stuck with 3E. But that doesn't actually help you. The only way WotC could even hope to woo those players away from 3.5 or Pathfinder is to return to the classic gameplay of D&D 1974-2008. But that's the one thing almost guaranteed to alienate the existing 4E fanbase.
Therefore, I predict one of three outcomes from 5E:
(1) It will be a very moderate revising of 4E. If they make some minor tweaks and get rid of dissociated mechanics, they might be able to win back some of the 3E gamers they lost. If they repackage the core rules into
a format which is easy for new players to pick up, they might have greater success in drawing in new players.
In this scenario, nothing really changes: You probably end up with a few players sticking around a vestigial 4E community, but most will make the switch. Heck, maybe the games are so inter-compatible that most people just swap material freely and it's only a few die-hards who really get up in arms about it (like the switch from 1E to 2E).
This is, IMO, WotC's best case scenario.
(2) They try to return to classic D&D 1974-2008 gameplay. On paper, it looks good. It looks even better when you say, "We'll return to 1974-2008 gameplay, but we'll try to incorporate all the stuff people like from 4E.)
The actual result would be a game that might have been a smash success in 2008, but is almost certainly a disaster now: Too regressive for 4E players; retaining too much of 4E to pull players away from Pathfinder.
(3) They push forward, creating something as radically different/advanced from 4E as 4E was from 3E.
This game might be great. Doesn't really matter. From a commercial standpoint, it's a disaster, too. Unlikely to appeal to a 3E fanbase already skeptical and cynical about WotC. Almost certain to split the 4E fanbase. Without an OGL to keep the 4E segment of the market alive, the players who stay loyal to that system simply exit the market. (Many are likely to leave the hobby, too.)
I really do hope that WotC can come up with some sort of magic rabbit that they can pull out of their hat. But, historically, new editions for RPGs which haven't resulted from significant, widespread dissatisfaction in the player base have usually had very bad receptions. The actual quality of the new edition is almost irrelevant in this, because what you're dealing with is a group of people with a deep emotional, experiential, and monetary investment in the existing product. Unless they already want a change, they are very, very unlikely to accept a change.