I don't think a modern setting fits CoH - too many high tech high range weapon systems (like ATGMs) and focus on merging combat roles like the Main Battle Tank or stuffing all sorts of heavy weapons on recon/infantry fighting vehicles (like Bradley or BMP). Or all infantry having standardized assault rifle + LMG loadouts.
While we would miss out on things like Heavy Tanks, it could still work. For example the Stryker Dragoon and Stryker Mobile Gun System could have a dynamic role like the Luchs and Puma in CoH2. Light tanks in general could be replaced by various Armored Cars and Infantry Fighting Vehicles.
Something early Cold War (the end of the 'mechanical' warfare era) would be pretty interesting though. Basically 1950s-1960s with Pattons and T-54s and with light tanks like the M41 still in service could basically be a reskinned CoH/CoH2. The same mechanics and core but in a new and unique setting.
Going with a Cold War setting would be dynamic, the Cold War as as much a jumble of technology as WW2 was. You could have a period where the US Engineers use M3 Grease Guns, the US GI use M16A2's, and Assault Infantry use CAR-15's. Or if you go earlier the GI's could use M14's and have M16's upgradable, or used by Assault Infantry.
All infantry being all-range always automatic weapons infantry also wouldn't add much to gameplay.
Well until recently the US Military used mostly M16A2's, M16A4's, and M4's, all semi and burst fire. I suppose that'd make them the long range faction infantry, and then whatever Kalashnikov using adversary is the enemy would be the close range faction infantry.
Honestly, it's hard for me to imagine CoH without AT guns. But the existence of World in Conflict leads me to believe it can work (but stay being CoH, not WiC, I much prefer CoH's cover proliferation).
I suppose it would work with ATGM Teams like the BGM-71 TOW or 9M133 Kornet, they would have to deploy like machine guns instead of being wheeled though.
I'd rather they'd stick to world war 2, there is so much more there that hasn't been fully captured.
Such as the Panzer III!!