As long as you keep the same kind of fun, fast gameplay and the granger, I am up for anything!
There could be the same area's of alien, e.g: Small fast alien, stealthy alien, big charging alien, jumping aliens and so on.
This opens up the possiblility for more buildings and and weapons (and aliens). You can personally balance everything and so on. Its a shame NS2 has mech suits, it would be cool to have them but it would cause quite a few people to get angry and shout "Oh god you're copying NS2!"
I do have numerous idea's for alien designs that I will post in the surgestions area when I get time.
Also, since there is no kickstarter, what are you doing with the reward items? Are you going to keep them and give them away if you start a new kick starter? Or are you going to sell them?