DANGEROUS WOMEN
Rose Wilson and Cassandra Cain I think create a interesting comparable given their history and parentage. I think as a pairing they'd be incredibly interesting and dynamic together. Their intense rivalry could easily become a romance. They could get paired together on a mission where they're forced to coexist together ( maybe reluctantly ). The bat family and Titans East are working together on a mutual problem that pairs the two together and the both of them have to work as a team. Rose could pose as though she is continuing as a mercenary and Cassandra under an alias could work along side of her. They could be infiltrating a unit of mercenaries who are moonlighting around doing various jobs for assorted villains.
Storyline could also be much more basic with them somehow pitted against each other and ending up in a life or death situation. I wouldn't mind exploring them coming into conflict with each other while Cassandra's under Slade's influence she comes after Rose by her father's orders. Another idea I had is perhaps they somehow both find eachother in a scenario where they're both in some kind of secretly funded private prison meant for meta humans and other assorted above average human's and they are bunked together.
CROSSOVER -- THE HAND
I think anyway you can envision a cross-over works for me, but to be honest I don't enjoy the idea of them just having always existed in one world without explination. I like the idea of Cassandra crossing over to the marvel verse though and resuming her role as Batgirl in New York City. I see it happening early in Elektra's life, where Cassandra comes into conflict with The Hand. I could go as far as to maybe Cassandra takes up Matt's role in her life at that time servicing the story as a huge "what if" type of scenario. Also I'd be willing to do it with Cassandra possibly joining the thunderbolts and once more having interaction with Elektra.
HERE KITTY, KITTY.
I don't even have a great idea for this but I'd love to do something with Catwoman and Batgirl. It's a pairing that just strikes me as interesting -- I imagine it can just be basic conflict in Gotham sort of scenario that could possibly lead to more. I just love the idea in my head! At the very least. Catwoman and her could have mutual enemy, or goal. It be a lot of fun to explore I think and I really love Silena Kyle and I could see her actually opening Cass up and helping her learn to cut loose a bit. I think it could play into the socialite gotham life a bit and not just be restricted to shadowy rooftop tryst and meetings...
IDEAL PAIRINGS
Stephanie Brown (favorite), Barbra Gordon (favorite), Ravager (favorite), Batwoman (Favorite), Catwoman, Elektra.