Let me just throw in a couple of thoughts before I forget them, although I haven't read whole thread yet.
About...
Endless lore accuracy discussion of Onra's map - It's not so hard to imagine that in a quasi-medieval world without GPS and all other knick-knacks, without known data about map projection systems, it isn't so hard to imagine that maps aren't always correct.
Nathalia Dravalor didn't have gps.
Just like http://cartographic-images.net/Cartographic_Images/109_Herodotus_files/droppedImage.png 'world' map isn't correct.
Common resources - while I don't have a harsh stand on this, I find it annoying when I have multiple versions of sujamma or gold bar or some Daggerfall book and even worse if NPCs don't recognise it for quest. So I'm pro-cobl or something similar.
Same worldspace or not - I prefer same world, but again everything has advantages and disadvantages. All the reasons that Iliana mentioned are good reasons, but sailing anywhere if priceless.

As well as riding in. In the end, it's a hard decision.
I also hope that different teams (I'm sure there will exist more teams on same/similar project)will be more firendly and sharing, but maybe that's too much to expect.
People always want to have something unique, exclusive, never-seen-before etc, but in the end they don't get the effect they wanted. Either nothing is released, or project is dead, or eternal alpha... or something else.
I had experienced that myself while making Morrowind drinks for Oblivion.