Well issue thirteen just says the ultimate villain returns not Joker maybe it's Doctor Hurt coming back if you remember the teaser page in issue one there was a promo page 
     
 
The first pic was the opening batman Reborn arc, the second was Revenge of the Red Hood the third was Blackest Knight now have we seen Hurt recently? Maybe maybe not maybe Hurt is coming back in that issue. As for Joker knowing Bruce I do think that was a major revelation that Bruce was Batman in RIP and maybe Joker now knows maybe  he hasn't shown up because Dick does not interest him maybe he is bidding his time planning something terrible for when Bruce returns or maybe I am wrong and he is making his return in issue thirteen. Like many other things in Grant's run I think the fact that Joker saw Bruce's face may be ignored.

" @johnny spam: Hurt may be Oberon Sexton. Than again , it could be the joker...than again, the Joker may just be keeping low, and could just make an-all-out hit on Dick, that could take him by complete shock. Honestly, I want to see Dick Bat (no pun intended) vs,. the Joker, or the Joker vs. the bad-ass Damian Robin! Huh :) "