Although he is Joker...
Joker is just a man in a suit. Clown make up, or altered skin depending on the version you go by, but in the end, man in suit.
So are Riddler (sometimes) and Two-Face. I don't think it's too far fetched for ss to make them. Most of Spidey's core villains wear/are green...most of Batman's core enemies wear suits. It all makes sense in some way.
Given what they've done so far for Batvillains (women, big guys and armor since they count Deathstroke) I can see ss attempting Manbat, Mr. Freeze, Clayface (he's a good guy now though), Deadshot and modern Harley within a few years if they don't do a movie version first.
We need some Robinses though.