Honestly I just today saw that World had sold like 14 million. I had no idea the game was so popular outside of Japan. Given that it does make sense to release future ones on both PS5 and Switch, but like a full Switch version, not some horribly broken version of the game and not some side game. It'd be stupid to not give Switch a full version considering that it dominates Japan and MH is one of the few mega franchises in Japan. Even just building the same game in parallel for each system, giving full resources to each system, would make sense, as the Switch version would pick up millions in Japan and elsewhere, while the PS5 version would sell very well in the west.
MH3G+MH4/G+MHG/X sold more than 17 million units on Nintendo 3ds alone. The core concept of a monster-hunting game was a ticking bomb that's ready to explode if it was handled properly. In the end, they pulled it off flawlessly the transition from 3ds to PS4, XB1, and PC.
Monster Hunter World together with Zelda BOTW is a good case study of how a great transition could help in elevating the series further critically and commercially.
I'd argue that they have had to do several transitions. Moving from PS2 -> PSP was a big change and they started to redesign the gameplay loop to fit handheld and ad-hoc multiplayer. Capcom has jumped through several hoops with the series and navigated platform change better than any 3rd party I know.
Given that multiple MH games sold in the 3-4 million range (physical only) on 3DS, and that Switch generally sells software much better than 3DS, I'd say there's room for a proper Switch MH to pull in huge numbers. Perhaps not quite as much as World, but enough to be an immensely profitable companion to the World series.
The franchise has never been bigger, and the thirst for a real MH on Switch (not just an old 3DS port a la Generations Ultimate) is intense. Capcom would be crazy not to capitalize on that.
While this is largely true, there have been several Japan-centric series not seen that big lift. 3DS is a bit underrated, especially since it followed the DS. The 24m+ 3DS userbase in JP is quite impressive. I don't think a MH exclusively on Switch would see 4m+ in Japan only, but would certainly outdo the 3DS numbers WW. I don't think we'll ever be able to test the theory imo, but there's no way the next mainline game will be exclusive to a single platform.