I think it could end around 10mil on Switch and 4-5mil on PC.

We resently got numbers for it right?

Just over 6million so far (sold+shipped & in stores) in just over a month's time.

Should break 10m no problem.

Safe bet is 10-15 M, game is coming to PC so it should reach that milestone

Tbh not that much other than QOL and graphical tech. The main change wasn't with the game it was how Capcom handled it much like with Fire Emblem where Nintendo began handling it like a big franchise Capcom began handling MH like a big franchise outside of Japan unlike before. 

Its already sold 6M on Switch in a month though...

I think he means an additional 4-5mil on Switch, since his prediction for Switch and PC combined was 10-12mil.

I'd say around 15 million.

Has now moved 7m

#MHRise has now shipped over 7 million copies worldwide, and we couldn't have done it without you! Check in with Senri the Mailman to claim Kamura Pack 3. 💌

As always, thank you so much for your continued support! ❤️ pic.twitter.com/3etXEx33cN

— Monster Hunter (@monsterhunter) May 28, 2021

So, tracking the announcements so far:

3/29/2021,  4 million
4/04/2021,  5 million
4/27/2021,  6 million
5/27/2021,  7 million

They are selling about 1 million a month at this point, but obviously the rate is slowing.  I'm thinking they will hit 8 million sometime in July.  This game definitely has legs.