You can still play it singleplayer so there could be a highest room and a fastest to certain room categories. And for CE there could be highest room damage less and maybe getting to a certain rank on a new account in public servers

with the way the category extensions leaderboard is set up it's basically impossible to add any ranked categories to it (or really any categories for that matter) so theres unlikely to be anything on there. on discord we were discussion having one for highest door reached and another for highest overall score. you can join the discord and discuss with us there! https://discord.gg/gx7sGguFG5

You do not need to add it to the category extensions, it is not considered an extension, it enters the main game and it is possible to add it to the main Roblox Doors main game. You can add it as a new floor