1. The Fractured Fanbase we have today
I do think it's a bit worse than it was when 3e came down the pipes, especially because 3e still has vague "support." I think that a clever 5e will harken more back to earlier editions.
2. Pathfinder's success/failure and how it affects the fanbase who didn't go with 4e
Pathfinder will probably be a modest success. I think Paizo would be the first on board if a 5e comes down the intertubes that they like, though, so I don't think Pathfinder would stand in the way of 5e.
3. The Bleak Economic Outlook
In 10 years, it probably won't look so bleak. This could actually contribute to the longevity of 4e: "Look at sales now! They're much bigger than they were in '09!"
4. 3pp's, and which ones are going with 4e versus Pathfinder/3.5/OGL versus those who choose to develop for any or all systems using copyright fair use protection
3pp's will be more fringe this time around than they were. I expect a lot of PDF's, and no big sexy hardcovers.
5. The PDF market vs. print.
I'd say the 3pp print market is on it's way out in the next decade. The PDF market should be okay, though, given the lower cost of doing business.
6. Illegal downloads of PDF's, taking into account the economy and ability of people to buy legitimately to support their hobby.
Blip on the radar. It won't hurt D&D any more than it has hurt the music industry (that is to say, it'll change the model, but it won't ruin a smart business).
7. DDI's success or failure, resulting in moving the game to an online environment or not
DDI, I'm guessing, will be pretty successful. Online support will remain key in 5e. I think the idea of gathering friends together is going to be at the core, though. What could change this is if the online game table gets more subscribers than the books get sales. Then 5e might be more about online play, with book support, than vice-versa. I don't think that's very likely to happen, but ya never know.
8. How that success or failure of DDI affects the bottom line at WOTC, which in turn affects their future development, balancing the bottom line vs. fanbase desires.
DDI's success probably helps them create a longer edition treadmill, too.
9. Th evolution of 4e, including but not limited to:
a. Miniatures-focused RPG gameplay, and it's acceptance/rejection
If the minis sell well, they'll still be an integral part of 5e (sadly). If they don't, 5e will still probably attempt to integrate them, but might also provide for more abstract combat.
b. Evolution of powers, dailies, etc and cards used for them during gameplay
If powers provide buying incentive for minis, then 5e will probably integrate them. If they don't, I would hope and expect 5e to dismantle the powers system and put up something quicker and cleaner.
c. Some sort of potential merging/morphing of powers/dailies cards, miniatures, and some Magic type card game into DnD, making DnD some weird hybrid of MTG, DDI, and DDM with some RP icing thrown on top of it.
I'd doubt that this move would be cemented. There may be moves toward it, but there are already moves toward it in 4e. Only if these moves are insanely successful will they dominate 5e.
d. Adoption and develpment for 4e by 3pp's, which takes into account the GSL's eventual development and attractiveness to 3pp's.
The GSL is an albatross. Even a "better" GSL won't win over 3pps that are already jaded and who may have realized that they can put out 4e compatible products without paying one bit of attention to what WotC says (or who have gone their own direction). A good enough GSL might win over some really good 3e 3pps to 4e, and thus improve 4e, but I'd think 5e would want to get this better from the start (maybe even going more open, if they're smart).
Different market, mostly.
11. 4e's ability to attract new younger gamers over the next few years.
If 4e fails on this count, 4e will be a rather large failure in the eyes of most of WotC, I imagine. 4e is supposed to be the populist edition! The edition that brings it out of the basement, into the living room! If 4e fails to do this, the 5e we see will be EVEN MORE SIMPLISTIC, probably. If 4e succeeds, 5e will probably retain about the same level of complexity.
12. 3pp's overall success, including but not limited to:
a. Some going out of business
b. New ones springing up
c. Potential merger some of some 3pp's
3pps are going to be hurting for the next 10 years, whatever happens. If they're involved in Pathfinder, it might go marginally better. If the GSL revision actually makes publishing for 4e appealing, it might go marginally better. But the greatness we saw during 3e is probably over.