I like this idea. I love me some Jill.Now forgive this, as it's a pretty massive reach, but it's just me mostly thinking out loud.
-As I recall Joker was ACTUALLY built off of Piranha Plant so it would seem like Jane is possibly our next character being built on top of Joker.
-All we really know about Jane is that she has a ponytail, and is like from a 3rd Party IP.
-In terms of female 3rd Party characters, it seems to reason that Jill (perhaps in her BSAA or RE5 Black Widow costume) could very easily be that character. She also has a gun that would work somewhat similar to Joker's.
-IndieGamerChick said that Jill had been considered for Smash and cancelled due to "political issues". Which could be political issues pertaining to her gun use on the base game (which seems to not be an issue for DLC as we have Joker).
-We have 3rd Party Mii Costumes missing from SEGA, Capcom, Square and Namco. SEGA's Sonic Mii costumes came back with Joker, and we're heavily rumoured to be getting a Square character of some kind, indicating Chocobo and Geno could easily return with the release of that character (as sales are much easier to divide on 3rd Party content when it's sold separately from the base game). Meaning that a Namco and Capcom character could also easily come along too.
-IGC ALSO heavily insinuated that Banjo would be coming to Smash. And if these characters had been decided on since prior to November, then it stands to reason that it came from the E3 sitdown Nintendo and Microsoft had.
A Fighters pass of Erdrick, Jill Valentine, Heihachi and Banjo-Kazooie seems fairly realistic.
Take that with a heaping bowl of salt but just throwing it out there as a scenario.
But I would be LIVID if they used that god awful mind control zero suit bull**** from RE5. That's like adding Dante but using the one from DmC. I however dig the idea of a BSAA alt alongside her classic design as the default.