I'm a huge mecha fan. The reason I find it difficult to answer your question is because you want me to prioritize
Seriously, the cool thing about the WWG mecha is the way they're modular and use a DIY-approach. You're not bound to only do a specific model, you can rather do a huge variety of different designs. That's very useful, imo. So you might want to add even more options to what's already there.Something which would be worth updating might be a somewhat lowered complexity of the parts - the Red Sector mecha are somewhat finicky, and among the more difficult models from WWG I've done (I can't say much about the PC Battleground models, haven't started yet). To a certain extent, this is because the instructions give you little in the way of how the parts come together, so it can be slow to figure out what goes where and how (a mech builder program, while probably not realistic, would be very cool in that regard).
Another thing I'd like to see would be added textures: not only primary colors plus black/white, but also grittier camo, tan or olive paintjobs.
My 2 cents.