I'm pretty excited about this race. As has been mentioned (and as is obvious), the small teams combined with the tough course make it a pretty broad spectrum of possible outcomes. Here are some of my thoughts:
Outcome 1 - Favourites until the end
If this is the case and the break has no bearing on the final, then it'll be a small group to fight it out, maybe less than 10 riders. This is the case where Valverde is the big favourite, unless Alaphillipe is also in the group. Riders with the ability to be up there would be the big guns - Valv, Nibali, Froome, Rodriguez kind of guys. But I think the chances of this straightforward outcome are pretty low, like between 10-20%, because there just isn't enough common cause to control things that tightly.
Outcome 2 - Late, strong break
This is, I think, the most likely scenario, like 50-70% chance. That would be someone like Costa or Kwiatkowski or Van Avermaet attacking, and some strong guys but secondary favourites from the major countries following (Rodriguez, Aru, Barguil). This could be where someone from a smaller country could capitalize, like the above mentioned riders, or Dan Martin, who has a decent finish. This attack would have a better chance of sticking if it went on the second last climb, or on the descent before the last climb. The bigger the group at the base of the last climb, the more likely it is that the best climbers are just gonna win the war of attrition. In other words, they probably won't let them away after the last climb has started, and the first attack will bring a response from the strongest riders, and then it's on from there. But if a solid attack happens before the favourites think it's time to spend energy, and if it coalesces into a strong enough break, it'll be pretty much impossible to pull back. Caveat: the climb is hard and long enough that the break doesn't have to be pulled back - if, say, Spain chases and keeps it to 30 seconds, I could see a few favourites bridging across.
Outcome 3 - Early break makes it/mixes with late break
This is the Olympics, so there aren't many weak riders, and depending on the makeup of the early break, it could go all the way. If some strong riders that aren't mountain goats (GVA again, or Wellens, or guys like Izaguirre, Cummings, Rosa, Mike Woods, Navardauskas, and on and on) get in there, they could be given some leash, and if the favourites' teams have riders up there (which, after seeing what happened in London, I would probably want as a favourite), it could go all the way, or be joined by late bridgers, or the favourites. There's probably an equal chance of this as scenario 1, or maybe even more.
That's the thing - I just don't know! So much will be determined by who ends up in the early break, and then secondarily, when the first real attack of the finale goes. This will be a tactical and unpredictable race, and I love it!
Who do you guys see going for the early break?