Or VR. As it's a "New way to play".

Probably Xcloud browser, technically that fits both a new place and way to access xCloud.

Cant see the Switch running Halo Infinite unless they stream it via Cloud.
I believe it will be an xCloud feature which technically makes sense.

Yep, he did say that just before the release of Ori 2 on the Switch

I would go with the VR option. I believe MS is still making moves in this area but it will not be a focus for the Series X. I still believe MS will introduce a partnership with Valve and or Facebook to support their VR gear on the Series X including their own devices. Having the MCC as one of the games supporting this new move would generate a lot of word of mouth.

That seems like an odd mix to me.

Switch is very unlikely imo.

Its much more likely its :
1) Cloud Based / streaming, either from themselves or 3rd party.
2) Its playstation 4/5 (these are powerfull enough to run the game, and the same achitecture ect, much less work porting).
3) VR option? for PC users.

Switch is 4th placed option, and much more unlikely.

It doesn't mention anything about a new platform. It says, "And maybe a new place and way to play." Much more likely to see VR, EGS, or the most likely reason is the customs browser they have been teasing for some time. MCC is not releasing on Switch or PS5.

It is either VR or it's a Switch version. And with a Switch version it's more than likely a cloud version seeing how recently games like Control and Hitman are on the platform via the cloud.

The teaser is referring to The Master Chief Collection (which comprises of Halo: Combat Evolved Anniversary, Halo 2: Anniversary, Halo 3, Halo 3: ODST, Halo: Reach, and Halo 4), not Halo Infinite.  The collection originally released in 2014.