It definitely won't happen for 1.20, but we do already have it on the wish list for 1.21:
Make verified multiblocks (alfheim portal frame, terra plate base, enchanter setup, gaia arena without beacon base) datapackable, but with plausibility checks
Although truth be told, it currently doesn't have a particularly high priority, since it's safe to add after the initial release, unlike some of the data structure changes for blocks, entities, and item.