Firstly I don't mean dividing the world map as it currently is, but instead adding lower level subdivisions to be used for certain game systems. Also yes you can subdivide hexes and maintain tesselation, you end up with 7 main subhexes that are each 1/3rd as wide as the parent hex, and you can continue to subdivide these subdivisions of course.
I also realize it'd require a ton of work, but ideas are cheap so there's no reason not to suggest them.
The main reason I want subdivision would be for combat. You could bring things down to a scale where individual subunit movement and combat is taking place on world map terrain, rather than the current window where that's abstracted away. It adds more nuance to combat, and would allow for subunits to fight across multiple types of sub-terrain. Plus it's just interesting to watch combat take place in a more direct manner rather than being abstracted dice rolls. Even when it is just dice rolls, like how MoO2's ground combat was.
It could also be used for city/zone management: When assets start taking up space, then planning out cities becomes more involved. Deadlock had each zone/region (Of predetermined and arbitrary shape/size) have one "City" view, which was a grid of tiles where all your buildings had to be placed. Trying to fit everything you wanted in the place that you wanted it required a fair bit of thinking sometimes and I enjoyed it a lot.
There's a few different ways to do this kind of thing as well.
One thought was drawing out subhexes during mapgen, so a single mountain tile would be drawn from its component subhex tiles. It'd mean the map's more varied, but would probably substantially increase worldgen time.
The other would just be generating a separate set of battle/city tiles based on a seed given to individual hexes or somesuch. So when stuff goes to subhex level it just generates the same subset of hexes for a given hex every time.
That's about it, thanks for reading