From what i have read online n64 and sega dreamcast emulation isn't really even that good on a pc. Maybe playable, but not good. So good luck trying to get those systems to run on a ps vita.
N64 emulation is commonly referred to as trash simply because it's not very accurate, but it runs most games with no issues. The PSP had an N64 emulator, which actually functioned fairly well for a low-spec portable. So it's definitely in the realm of possibility. Someone is developing a fully accurate N64 emulator (like higan) for PC, called CEN64, but (like higan) that will require a beefy PC.
Dreamcast emulation is more of a matter of lack of dev support, people sort of lost interest in it years ago. Reicast is the latest Dreamcast emulator that's actually (somewhat) worked on, though there hasn't been any major releases for the past year or so. But it's still a decent emulator on ARM devices which, conveniently, the Vita runs. But I don't think it has the processing power to truly pull off full-speed DC emulation regardless.
As to the announcement, I honestly have no idea what it could be. I highly doubt it has anything to do with actually developing/porting an emulator of another console. I'm half expecting a major Vita SDK update more than anything, or perhaps a new version of Vitamin based off of motoharu's work on creating complete dumps. That would be amazing, no more potato dumps and would fix those problem games like Axiom Verge not being dumpable.
If it was an emulator, though, I'd prefer a port of DraStic more than anything. Would be easily doable on the Vita, it's definitely powerful enough to run a vast majority of games no problem. Unfortunately that likely won't happen unless Exophase makes DraStic opensource, or gives The Flow the source to port it himself.