Unique Overworld Boss (a la DoomGaze)/Creating New Area Question

Don't the aforementioned patches simply alter the pointers related to the calling of the particular functions involved to free up space?

Yes, this is exactly what those patches are doing in USME. But as for a similar way to go about doing that for the map data, I myself have not a clue. If I had to guess why nobody has done this, or why there is no patch for it rather is it might just be much easier to move or re-point a bunch of dialog related stuff, and a whole other thing to move the map data. But like I say, I'm just not sure.