It's more about the new character and playing up the Joker element in a different way, not just giving a character another one's powers. 

We've also got plenty of Gotham centered heroes ATM, so I'm not sure a Joker would make things better unless he was based somewhere like Hub City. I found this picture from a Batman Rebirth issue of Punch and Jewelee looking a lot more badass. Could make Joker and Harley Quinn a crimefighting duo in another city...

[img]http://static1.comicvine.com/uploads/original/11125/111253436/5599981-17a.jpg[/img]

~KL~