They should tell Mousasi to drop to middleweight because as well as Jacare, there's then two guys who they can say would have beat Shields anyway. With Shields in the UFC, he wont be able to prove otherwise.
Perhaps they should do a tourney with Hendo, Jacare, Mousasi and Lawlor. I'd expect Mousasi to win that and think Jacare could beat both Hendo and Lawlor too.
As for Shields in the UFC, I think his takedown ability will look a whole lot different when he's fighting someone a bit more agile than Dan Henderson. Despite Dan being a high caliber GR wrestler, he's quite slow and flat footed, and I can't see the likes of Fitch and GSP being there when Shields shoots as much as Hendo was.