I don't know what that would entail.
I meant that I'm interested in making 3D art in collaboration with you because I think this game has potential to sell well.
Well this game could certainly benefit from having some more assets. If you make something good, I'll gladly put it into the game and credit you. It's really lacking objects to hide in and different levels to play. Adding human characters requires an embarrassing amount of extra work, but it would probably add to the appeal.
If I made you a collaborator on github you could add/remove/change stuff in the project and request to merge your changes with the main build, but you would need to use git for that. I'm spending most of my time working on my next thing, but I'll totally switch back to this if something interesting comes up.