As for Umbar, assuming the plan is indeed redoing the entire Gondor on After and there is no way in the world they would move everything North to give Harad/Umbar some breathing room on
that map, then I guess this is the best (and most likely) option for how to handle map situation:
- One massive border/invisible wall/teleport border on sea.
- Harnen as border, with one or few teleport points where appropriate.
- Housing area with open-space invisible borders, like Breeland Homesteads now. (But upon entry actually ports you to housing in old Gondor space, and yeah, hopefully with new terrain changes brought over : )
- On brand new open world map, as in "region 6" "the South", Umbar space initially in its own bubble, but well-placed so enough space North for all the ground that needs to be covered to Harnen. And with some foresight... put in the top left corner of the heightmap file (though with some wiggle room for expanding sea borders to the West, just in case for whatever reason, for boat action, cursed Othbreaker vessels, or maybe if they ever have ideas for some island expansion in these Southern lands?)
- Proportion-wise, as I very roughly demonstrated, Umbar bay may be expanded quite a bit for cool worldbuilding and immersion purposes (come on, those Corsairs war fleets, present day or flashbacks, gotta have
some space on the waters! The way it was done in Gondor was incredibly cluttered, fine back then, but a bit too cluttered if you wanna have player boats or scenic Corsair landscapes). Since it would be on another map, after a teleport, wouldn't really be too jarring, if the bay was overblown compared to what we had in Gondor for such places and coastal areas. Not much different from overblown Mt Doom or Evendim.
Now, if Umbar is like in addition to Gondor landscape (??) as part of one expansion (?), which is still a bit weird and unclear to me whether that's what Scenario meant, I guess the size of landscape on my roughly done picture above seems too insane and impossible - but, but... if they're smart with these boats and if they're actually making traversable/quest-able water a reality, then the realistic - and still sizeable, impressive, scenic, COOL scenario - may be to do just the BAY ALONE, as in expansive water in the bay, with bits of shores here and there and the city/smaller surroundings. Now, THAT I can understand. The Northern mountains of the bay might create such a neat barrier and we don't even need that entire northern bit of land initially. But then they can easily grow the world around Umbar from there and fill in the missing pieces of the puzzle, oh and also take that land (and sea) route back to Gondor. Though maybe we could also take a "quick ship" back to Pelargil and get back to Nurn from there at some point too or someplace else, so it's not like 2-4 years dedication of growing the South alone.