An idea I got from Monster Hunter Cross/MHGen, where there are some endgame variants of normal bosses that have separate equipment, be that armor or weapons.
So, say you have the 4* Snarble Barb, instead of going for BtB, consider going for the new Shadow Lair variant, with lower attack but added poison.
Or possibly SL Shields, so instead of going for CoA, upgrade your Blackened Crest into the Shadow Lair variant, with much much lower defense but has an attack boost.
It would give some more meaning to going on SLs, especially if there were multiple weapons per lair, like if the Snarbolax SL had a Poison Bomb, a new gun, and a poison sword, or if say, Darkfire Vana had a new shield with low stats but an attack boost, a hammer with super high normal and some added shadow, or a new revolver gun, with high normal and some shadow. Roarmulus twins could get some new fire weapons, and JK could get some new freeze ones.
If they're given some good stats it'll give reason to not just use HoH and occasionally Basil for weapons, and SLs could be ran for more than just some crowns and radiants.
You could even have them require new materials if you wanted, or make the new ones only drop on elite difficulty.
SK is pretty deprived of endgame content at the moment, this would make some of it slightly less stale and hold players over until new bosses/levels are added.
+1