-Have an option to turn soulbound gear piece from old content (current tier items should be unaffected by this) into "Transmogify" tagged item, stripping it out of all stats and making Bind on Account. PvP gear behaving same way, season 11 and down are elegible for this and stripped from stats as well. This service could be available at transmogrifier vendor for 50 gold per item fee. Change is permament and irreversible.
It will alleviate 2 pains at the same time
-Freeing lots of bag slots on main characters. Some people have thirteen tiers of gear there.
-Making farming old content xmog bit easier as the drops would be account bound and you could pick up e.g. mail chest on your mage to xfer it to shaman. I'm looking at you Freya10, 18 runs (six months!) and b!tch still didnt dropped my chest.