It can be anything
My Focus is on building platform / environment for modders not for players. If you like concept of converting any possible game idea into space ship with two unique abilities, then go ahead and contribute even when its only an idea.
Imagine mod in which units are based on starcraft in regards of gameplay not graphics. We need for example burrowing ability for zerg ( which is API to chsnge type of unit to another one) or life regeneration when close to base. Protos needs shields and terans fire on damaged ships. So if you need some new API just let me know.
I am not going to reject any future pull requests which are not directly againts rules defined in first post.
Regarding data my only Focus is on sc2 mod. If you like IT you may update arts already exist in the gamę or provide feedback about gamę balance, which at that moment is non existing. My mod would be vanilla data to help invite more contributors. But after that i want Focus only od moddability and core features.
I hope i have answered your question
Another example is ww2 mod
We need API for different Control method for tank / plane / soldier. Rotating turrets. Running crouching and jumping for walking units. Fiction based on terrain ( in space IT is constant ) and different collision model. Same with plane with minimal velocity and ability not to collide with land units ( check total anihikation )