Depends how far into CW timeline you want to go.
As for a "true/interesting" CW game, HoI will allways to much fokused on WW2 stuff.
And to change gameplay into getting interesting CW features, too much needs to be added/changed maybe.
You need nukes and stuff around much more detailed(strat subs, ICBM.. SDI), ship combat with missles exceed numerous current HoI prov sizes, planes moving at supersonic speed need ajustments for combat in the provs too(CAGs..). Thats already quite some big changes "under the hood" only for combat.
And then, spacerace, spionage war, economic... I doubt it, it will be easier to design a complete new game around it. And afaik there is a CW game under development. So that niche is getting filled already.
But
as HoI2 had already an Add-on that extended the timeline for a possible third WW(timeline up to 1960), that might be possible for HoI4 again imo.
Small changes to the engine could be done easier and would still fit into the HoI game philosophy.
Same for WW1(timeline 1905-1920). Afaik that mod for HoI3 has among the most downloads of the bigger Mods. Not much talks, but many download it. So it could also be a good selling dlc.
Next to that, imho it would be easier to adopt the engine to that kind of timeline. Intermediate time would not needed to be filled. Mods could do that if wanted. But new mechanic/features would be needed to have a more "WW1 feeling".
I'm all for it, expand it later to WW1 and "WW3".