I would love to see a H4H series done using the newest version, led by Misty Knight. It had the coolest lineup: Ghost Rider, Iron Fist, Moon Knight, Punisher, Black Widow, Paladin, Falcon, Silver Sable, and Elektra.
When it comes to animated films and cartoons, DC just does an amazing job (not saying Marvel isn't good, I've just never found a piece of DC animation I've ever disliked) and I think a Nightwing cartoon would be incredibly successful. Especially since Dick Grayson is one of the most recognizable DC/comic book characters in existence and although Dick as Nightwing has had some decent screen time before (most recently in Son of The Bat and Young Justice season 2) a lot people would probably be really excited and supportive of him getting his own show.
There was even talk about Nightwing being given a live-action TV show adaptation like with Arrow, Flash, and Gotham awhile back, but so far nothing's come of it.