I don't even think AC will make it out before Fall now. After Golden Week, it's gonna be slow season any way. As long as there are some decent game (100K+) coming in a consistent flow, 3DS doesn't need any blockbuster games. Besides, Oni Training is coming in the summer and has a chance to turn into a hit.
I don't think it'll have much effect. It really doesn't seem like Koei cares to "expand" the reach of their Nobunaga's Ambition series - the idea for this crossover didn't even come from them (they originally proposed wanted a Musou game, IIRC, and the Nobunaga idea came from Nintendo's side) and seem to prefer to appeal to the usual fanbase of that series.
Just look at how, besides being a Pokemon crossover, this is the first game in the Nobunaga series that used the Samurai Warriors versions of the characters, rather than Nobunaga's usual more down to earth takes on the cast. If they were worried about expanding Nobunga, you'd think they'd have attempted cross promotion with Samurai Warriors before, considering how that's their best selling Warring States era series.
I highly doubt it can't handle it. I think it has more to do with Capcom trying to gouge which fighting game to pursue on which console. SSF4 did reasonably well, but I think they are aware that they need to do more than just what they did with that game.
It looks like a great combo for June and July since they will probably have good legs. I expect Mario Tennis Open to sell over 500k units and Dragon Quest Monsters: Terry no Wonderland 3D to be the fourth million selling title on the 3DS.
Unfortunately nothing suggests Kingdom Hearts 3D: Dream Drop Distance has had an impressive debut, I wish I'm wrong. An opening below 300k units would be very disappointing.
Yeah, of course they're bound to throw out some good quality new stuff, but we don't have a clue about which games, although we may assume a 2D Mario is to release in November/December along with a budget edition of MH3G.