Beware: the post you are about to read has rampant speculation and little grounding in reality other than what an armchair runner (me) has read on this thread already. But I'll pipe anyway...
1. Hall-relatively few performances at long distances, but has yet to have a truly bad day beyond 12k (that I can recall, I'm sure any number of posters will happily correct me if he has...) and obviously has the speed and fitness to be with the best at mile 24 in London on a hot day. Good cross-country performer bodes well for hilly course, as does his training location.
2. Sell-consistency and doggedness make it hard to conceive of a race in which he isn't in the mix for top 3. I can imagine him winning, but I have a hard time picturing him finishing out of the top 5 based on his consistent performances and his ability to run 2:10 all alone at Chicago on a windy day. His one off day at the last trials wasn't really off as much as gutsy, and almost seems like it has since been shown to be a harbinger of things to come...
3. Abdi-Got it really wrong once (NYC) and right once (Chicago). Seems to be in great shape at present, so the odds are on getting it right this time, but not quite so sure the hills are really his thing as he's never been quite so thrilled to run cross.
4. Meb-hard to imagine him out of the top 3, but doesn't seem totally healthy, so hard to put him ahead of Hall, Sell, Abdi.
5. Gilmore-consistent improvement and steadiness put him in the group that's likely to move up late. If enough people blow up he may run into contention.
6. Ritz-seems his training is going well and he certainly sounds like he is better prepared for this one. If his long runs are going as indicated he may be a real contender, but his one prior attempt leaves little indication of his ability to gauge the effort. On the other hand, his cross-country abilities bode well for the hills.
7. Culpepper-little to gauge his fitness on right now, but a smart runner who is unlikely to totally blow up. If he has really returned to what worked in his first marathon, he might be more of a contender than his recent results indicate.
8. Hussein-consistent, but slipping from his prime.
9. Verran-see #8.
10. Browne-total shot in the dark here, he hasn't competed at this distance successfully in so long.
KK will either get top 3 or DNF. I hope he comes in the top 3, but can't imagine trying out new orthotics in racing shoes in the final two weeks before the race. That sounds like a recipe for disaster to me, so I'm going with the DNF. Greatest marathoner on the planet for a stretch, but at the moment it looks like that mantle is long gone.
As much as I'd love to read a story about the success of Leslie or Nuci or any of the other candidates, best evidence suggests that it boils down to the runners above. My less precise guesstimate would be: two of the three spots will go to Hall, Meb, Abdi, or KK, and one of the spots will go to Sell or Gilmore.
If one of the runners that hasn't completed a marathon can pull off a debut like Hall, sure they could be in the top 3. But if they can pull off a debut like that, why haven't they done so already? Seems odd to leave it to the trials, the one race where they can't even get an appearance fee. Or at least I don't think they can.