I'd 100% retcon SL in terms of what we saw and how the SL works, I think we can keep parts of it like some characters and whatnot but for sure all the shit with the dumb robots, first ones, Jailer nonsense of "since WC3", Zereth, Elune and so on should be retconned.
Maybe an expansion can deal with parts/a zone/single minor covenant of the SL, but never directly with it and we should NEVER go into the SL itself.
Though I'd also go back into BFA and retcon Azshara/N'zoth so they can get the full expansions they should have gotten. BFA should have just been fully about the fourth war and Azshara coming in the final patch to lead things into her full expansion that would then lead into a full old god expansion with N'zoth.
Honestly, I'd also make some changes to legion's final patch so that the final patch became an entire expansion of it's own as it should have been.
There was so much potential there that was wasted in one patch, e.g. a full army of the light (with more than just draenei), argus, turalyon/alleria story, us using the crystal to invade legion worlds (i.e. us being on the offensive after we kill Kil'jaden and weaken the legion), more presence and story with Sargeras, much more titan revival story/characters, legion final raid and so on.
but nah, all that was wasted in single patches so Danser could push his stupid waifu sylvanus story and push his garbage lore of SL on us.