The FOG :
The fog would be deadly. Anyone within the fog would die.
The fog would cover X% of the map (>=25% to be effective).
The fog would move once every X days.

Pros :
The map would be reduced, but no part of the world would be destroyed.
People would need to move regularly.
Localized ressources would be unobtainable for a short period of time, making trade happens.

Cons :
Local banking
Holdings

PS : This is not a troll , map is too big!

Honestly kind of a cool and clever idea to adjust map size to current pop.  I agree with the cons though, they'd need to be addressed.

Could even be a source of Conflict... some kind of racial battleground results could influence which racial territories get "greyed" more.  Or some variation.

I like it, it'd be fresh and new.

But it'd be a lot of work (which Uber aren't exactly known for), and there's too many things to consider.

Lol, force more stuff on ppl. Same dogma! People are bad, they don't want to trade! They destroy the economy holding on to resources! Let's force them to trade!

(People don't wnat to live close to us! They are so mean! Force them live close to us and force them to come to village pvp or whatever there is! - Same shit.)

Like that worked out so good so far.