I’m speculating, but I’m of the opinion it won’t be until monorail guest capacity can increase and they can accommodate the extra traffic on the MK Resort monorail line that the Epcot line creates.
I suspect Disney doesn’t want to run both buses and the Epcot monorail to provide monorail resort transportation to Epcot - so it’ll be at a point where they either can or want to make that change.
Or maybe when all monorail resorts are back online.
Who knows though!
I hate to say this out loud, but as a frequent monorail resort guest, I have actually enjoyed busing instead of monorail, especially at CR and GF which normally require TTC transferring. Our experiences with busing to Epcot have been quite pleasant. I’d still rather have the Epcot monorail in service for the cool factor, but I haven’t really missed it.