It's a possibility.

It's not out of the realm of possibility, and would reduce the need of having a character like Gaim or Den-O be 5 different characters in one.

I know I wanted to get into Battride War 1 & 2 but decided against it since playthroughs I saw showed nothing but the story, which wasn't too much of one. All those games feel like are just quick opportunities to use your favorite Rider's powers & not much else. There's no VS mode. Why???

I can understand that.
But fighting games aren't the same. I know it seems simple, but a lot goes into them. It's more than just having a lot of characters.

I expect some thing on the Marvel Vs Capcom line since Kamen Rider in my eyes would be super crazy hard flashy combos on the screen.

It would make sense. I think putting it closer to the simpler gameplay for MvC3 would be the best bet.

Absolutely, it's difficult properly make a system that functions well & is fun at the same time. Not to mention balance can be a pain when the franchises you're making games of aren't fair to their whole cast of characters in terms of ability. I just don't get why they felt the need to change what Climax Heroes was since its inception. Were the games not doing well after a while? I don't know what the future holds for the games & if we'll ever get another fighting game for KR, or if Summon Ride will just be all that remains for however long. I wouldn't think so since KR isn't as popular worldwide as Disney (no clue how Skylanders does internationally), but I could definitely be wrong.

It's likely simpler than making an entire fighter from scratch. Or it'll probably make them more money.

Namco Bandai can just make a Toku all stars game with fighters from Kamen Rider, Sentai, Ultraman, Godzilla and Gamera. Namco Bandai owns the video game rights to those franchises and are market to kids in Japan. Imagine Smash Bros but with Toku characters.

The thing with that is you'd have mostly current Toku characters taking up spots, meaning you'd have to carefully pick & choose who else from the past would be featured & it creates disappointment for people who don't see their favorites represented. The appeal of these kinds of games (at least to me, anyway) is seeing generations clash. Plus seeing monsters munch on the various helpless henshin-heroes is completely one-sided. XD

I really don't think that'd work.
Mainly because it never works.