I mean if people started paying us to prioritize certain additions over others that would sound pretty exciting to me :P

Anyway. Uh, probably the biggest thing that someone outside the JJ2+ team could do, outside of drawing such tilesets in the first place, would be editing MLLE or WebJCS to be able to understand and use those files. (Otherwise the JJ2+ side of things would be even less useful than the vertically-flipped tiles code, which also no level editors currently support.) Conceivably there could be some discussion about what the new file format would look like, but I'd guess even a very basic edit of the j2t format that simply dedicated 2048 bytes to every tile image instead of 1024 would be sufficient.