Don't forget the one time Quinn Duffy said they could take the franchise anywhere in history or future.
Vietnam or cold war gone hot would be fun and still hold the Coh basic gameplay and charm. Guided misses wouldn't be in mass, Lavs and Humvees would be useful, still hold light tanks and MBTs, introduction on helos (transport, scout, heavy), flashbangs, fast ropes, shotguns?, gas masks?, napalm, tow at guns?.
There's lots of stuff that you can translate over.
https://www.reddit.com/r/CompanyOfHeroes/comments/biv97b/coh3_will_be_modern_warfare/em4pwaa/
I agree completely. Planes /attacks helis/ UAVs can be off map assets and the infantry close combat one of the highlights of this setting.