There are some future characters figures who we know Sideshow and HT will have trouble with: Thor, Winter Soldier, Falcon, and War Machine. It's too early to call on some others but I suspect they won't move well either such as Quicksilver, Scarlet Witch (potentially 3 versions up for grabs), Vision and Ultron. I really want Ultron but I'm tempted to wait until he goes on discount.
But yeah, I started collecting about a year before things started selling out. Now you can pretty much wait for a discount on anything except Iron Man. I'm actually really surprised that Sideshow hasn't done bigger diso****s on War Machine Mark II and some others. The price is just way too high.