I've been thinking of routing an All Treasures run of this game. If I complete a run, will a category get added, or would it only get posted here on the forums? Thanks.

I doubt it would happen, mods will jump in and give their verdict but general consensus is that categories won't get added by the mods unless it'll be popular to save on clutter on the boards, and I personally can't see it being a popular category for this game!