We seem to zoom out to a market view and back down to the individual player level in this conversation a bit. Here's another observation from the player level:
This morning I shared the elevator with, among others, one of our grad student assistants. I'd heard he played D&D after forming my initial group to run through the Starter Set. I know he wants to play, so I invited him to jump in when we start Hoard of the Dragon Queen. He said he would love to join us. Now at our floor, walking to our respective work areas, we chatted about his gaming history. He's played only Pathfinder for the past few years, hates 4E, and would really like to continue playing Pathfinder. He seemed a little sad (but accepting) when I let him know that Pathfinder isn't under playing consideration for our group unless 5E turns out to be something other than what it seems. Several members of our group have indicated a preference for 1E-style play, and a Theatre of the Mind vibe. To my mind, this is where the competition happens.
My observation from a DM/GM level:
I've run games since 2nd Edition, and by that I mean there has rarely been a time since 2nd Edition came out that I have NOT been running a game (I started PLAYING a bit before AD&D came out). I enjoyed 3rd Edition a lot
as a player once I had wrapped my head around it, but when I ran a 3.5 game for the first time I found it very difficult to keep the challenge level up for the players. There were several reasons for this -- we had a large group, we were joined by one or two real powergamers, and the rapid expanse of the internet spawned things like character optimization boards that made it relatively easy for even less prone players to whip up very potent "builds", or harbor rules exploits under their cloaks to be saved for emergency situations.
I found it tiring. It probably didn't help that by the time I ran my game, even 3.5 had had years to sprout splatbooks and bloat. By the time that game ended around level 16 (I had run it biweekly for years by that point), I was disillusioned with the system.
For my next game, I had planned to end things much earlier -- by level 12 or so -- but wasn't going to tell the players that. I just wasn't into how the game played at high levels. Lots of bookkeeping and room for rules exploits to crop up.
JUST before that campaign started, I read about E6, and fell in love with it. I convinced my play group to give it a whirl, and they were into it... for a while. But they lost interest maybe 5-10 feats after attaining level 6. We ran the campaign to 6+20 feats, but suffered from player attrition as people, in retrospect, got bored and dropped out (still, we were able to finish the campaign to its conclusion).
I decided to raise the bar for my next campaign -- the one I am running right now and about to end. This would be Pathfinder, which seemed more streamlined than 3rd Edition, and I ran it as an E8 game intending to only go to 10 "epic" feats. I think this would have worked well but unfortunately due to a math error I had the PCs gaining epic feats at four times the recommended rate, and by the time I had noticed some damage had been done, and my quick fix only dropped feat progression to double what was recommended. Once again, people got bored around 5-10 "epic" feats in, and we suffered player attrition as people dropped out (there were reasons other than getting bored, but I'm sure getting bored was a part of it).
My intention was to run a Paizo AP "Carrion Crown" next, maybe as an E8 game with mythic tiers thrown in, but at this point (most of) my players are pretty much burned out on E# and have said so. Also, a player in a related group I play in went out and bought "Carrion Crown" to run with his another group, and one of the players from THAT group recently joined my own, so running CC was sort of taken off the table. I was thinking of running the upcoming Iron Gods, as a straight-up AP with no 3.5 material allowed and some other restrictions on gunslingers, etc.
And then I saw a post where someone mentioned that 5th Edition was similar to E6 in some ways. And I checked it out (I had previously had no real interest in 5th, having switched to Pathfinder when 4th Edition came out because 4th didn't appeal to me and PF had been there looking like such an improvement over 3.5).
My players' reaction has been mixed. I'm going to offer to just buy them all the 5th Edition PHBs so money won't be an issue; some of them seemed interested when I spoke to them, some of them mentioned concerns about cost.
I'll pick up my own copy of the PHB and read it through before making that commitment though. If I do, I will likely be running Tyranny of Dragons as it comes out.
I'm liking the simplification of rules that seems to be coming with 5th Edition. I like that it is recognizable as having essentially been built from the same chassis as 3rd Edition, which I am familiar with (4th Edition never felt like that, and it lost me in large part because of it). I'm liking the restrictions on buffs that should get rid of a lot of the time players spend decking themselves out like Christmas trees with buff spells, the time I have to spent keeping track of who has what buff for how long, etc. I'm liking that Teleport is now a 7th level spell, and the implications that that brings for the other "easy travel" spells. And to a degree I'm just liking the idea of jumping on to a new system before the CharOp folks have a chance to pick it apart and break it, before the inevitable slew of splatbooks comes along to make it easy for them to do that, before my own players start to get TOO savvy to the rules.
Because right now, working full time and caring for four kids, I don't really have to time to pore through the books and regularly visit forums looking for ways to challenge a large party of well optimized PCs in a straight-up campaign of what Pathfinder has become.