DA

I'd be willing to bet that it would be a Western-based book, movie, or tv show fandom; I don't think he's ever shown any interest in any Eastern-based canons. While I wouldn't completely rule it out, I'd also guess that he wouldn't go for a video game fandom, since it would take so much time and effort to consume the canon. I've noticed he also takes to canons involving some kind of fantastical element (only exception to this I can think of is Hornblower?) that have large-to-mega fandoms surrounding them.

I'm genuinely surprised he's never tried to get into Dr. Who.