The Totenreich cutscene specifies our next location will be a 'place of fire', just like with Paradox that said we needed to go to a 'cold place'
Takeo is the last of our OG characters to get his soul back, and the volcano map was said to take place in Japan
When the original map line-up was rumored (Nuked NYC, Vietnam, etc.) they were all later debunked with the exception of the volcano map still noted to be in the works. With how they've done the side EEs thus far, it seems they took most of those original map ideas and scrapped them into these EEs
Let's be real, if they want to go bigger and crazier than a Norse fishing village with a giant, what better than to explore the temples of Japan next to an erupting volcano? Shit would be legendary