I can just hear the whiners now: "We have the WHOLE WORLD that can participate in this (dynamic campaign) war!! Why doesn't the DC engine take into account that [Russia|China|US|whoever] is just a couple hundred miles away, and they can be included?"
I think that the complexities of trying to build a map-based (read: confined space) dynamic campaign engine is, according to DCS/Eagle themselves, hard. It was part of the roadmap for 2021, but that has clearly be re-prioritized, largely (I suspect) on the difficulties of making it work they way that they want it to. Add on top of this the fluidity or "open world" sort of possibilities of a world map, and there is a lot to consider.
In addition, an 'open world' sort of ability within DCS, while a noble and worthy cause, is going to be initially met with the screaming, stamping of feet and griping, that the aircraft/armies/equipment of [Insert My Favorite Country here] are not properly represented!! <rage!>
Don't get me wrong. I'd love to have it. I just think that an open-world DCS is going to require a LOT of help in development from modders and third-party content providers.