4. A Battle With His Henchmen
If Warner Bros. has decided they'd rather save The Joker for Suicide Squad (which makes sense, especially as that's one of the most compelling reasons to watch the movie right now), then there's still an indirect way he could factor into Batman V Superman; his goons. Batman coming into contact with The Joker's thugs at some point could be a nice way to not only hint at the fact that he's still out there somewhere, but that Bruce Wayne is currently actively hunting him down by going after his men. This is something which wouldn't even need to be directly addressed; instead, the movie could just allude to the fact that finding The Joker - or at least cleaning up what remains of his men - has become something of an obsession for the Dark Knight, one that's ultimately replaced in this movie by his need to take down Superman. We've already seen that The Joker utilises uniquely dressed thugs to do his bidding in Suicide Squad, so Batman taking on remnants of them in Gotham City would be a fun way to link the two movies in a fairly clever and subtle way. Rumours of The Joker killing Robin would no doubt have spread throughout the criminal underworld too, so someone Batman encounters taunting him with that information would be an awesome way to then show the vigilante losing control and beating that person half to death, something which soon winds up on Superman's radar if that trailer is any indication.