Weight will be the drive for the next year or two, I think. Efficiency will be the necessary follow up to this, since such a large part of the whole gun's weight is attached to the bottom of the gripframe. More Durable hoppers could happen anytime, although there is a balance point with something like that, where you have to find the ideal compromise between good reputation for reliability and something that won't last forever (so that replacements/ parts still sell). That probably applies to guns, too; durability will be the last metric to get refined.
I agree with Manike about the consistent paintballs. That would matter a lot. It may be that the most important developments are not in the technology used on the field, but increased efficiency in the infrastructure of paintball companies. As logistic expenses dwindle, profits increase, and sponsorship/ savings trickle down to Joe Paintballer. Or more can be earmarked for R&D. Or else Richmond Italia finally gets that gold toilet he's been wanting...