According to Tokusatsu Network's translation of the Figure Oh scans, Kusaka's return is supposed to be a big deal for Takumi's role in the movie, along with a meeting with an as-yet unknown Showa Rider. And it makes him question his path in life--which could be a really interesting bit of characterization, given that Takumi should have died eleven years prior--the final moments of the finale certainly felt ambiguous enough, like he realized he was living on borrowed time.

Maybe there's some truth to my fic-theory that "Riders never die" after all.