Eh, I don't think all mainstream MMA fans are as dumb or absent minded as forum goers believe. Strikeforce wasn't some hidden gem. And the internet is widely accessible to everyone - if someone sees Mousasi is headlining a UFC event, he or she is likely to go online and look for information. I think we underestimate how much the 'casual' fan knows. Look at the reactions Cro Cop and Rampage got when they came over to the UFC. And this was years ago. People may not be aware of Mousasi's vast history, but I'm sure they're aware of who he is and the talents he possesses (or lack-thereof, according to some). It isn't a chore to pull up old fights on Youtube.
But then maybe I'm just too optimistic.