[@Martian]: Hmmm. I feel like it's a bit hard to justify why he'd end up in Japan(which has a lot of its own heavy kaiju research), since if anything it'd make more sense for him to go to the US which would be more familiar ground for him anyway if he's studying what's almost certainly a purely North American entity.

As for the kaiju ideas, I want to keep this strictly to Toho monsters and originals, so as to avoid questions on why I'm not including lots of other franchises in the mix which could get a bit messy. The closest to any crossover is King Kong(as referenced in the OP), but he's already a Toho kaiju anyway.