heh funny, i was just about to post a summary of this thread in the tidal discord channel and while writing came to the same conclusion as you: custom OSC messages and a message handler on the supercollider server could possibly sort it out.
i also think that this reframing of it being an issue of needing an interface to receive scheduled OSC messages as opposed to an issue more closely tied to superdirt/tidal should make it reasonable to open a github/git.iem issue with the developer and possibly work together on a solution
i'm not sure if supercollider can receive simultaneously on different ports though? time to make some coffee and experiment some more i guess
are you on the discord server as well?