1. With version 1.6 being soon approaching (on the 19th), there will be a temporary embargo (suspension) for runs running on the new patch (old patches are still okay). This will give time for people to get a feel for it, for any potential bugs or rulings that need to happen.
2. Also, if you do happen to have any ideas on additional categories with the new changes, please create a thread in the forums or in the Discord #suggestions. (Discord is more visible than here.)

Can multiplayer runs still be done on old versions? If my friend and I both revert to 1.5 and do a perfection speedrun, will the multiplayer function even work on 1.5 anymore? We’ve had this run planned since early February and now we are afraid this will kill it (both the update and the inability to do runs on 1.6 for submission for the time being).

Current Perfection is for 1.5 so you can still do that and submit. More than likely there will be a version selection or have it split between 1.5 and 1.6 versions. (No current discussion yet from mods/community.)