Has map cacheing been improved?

Has map cacheing been improved at all? Last year I started an action rpg with the map editor using a multiple map system of traveling back n forth between maps... But it didn't work the way I wanted it... Is it possible to make a campaign like the Orc Frozen Throne campaign with traveling back and forth between maps?
And if so, does it work in multiplayer?

Yes and no
It works single but not multiplayer.

What about via code editing?

Does it work in multiplayer via code editing? No. There's no way to switch maps in multiplayer.

You can, of course, simulate it by making different areas of one map into sub-maps.

But that could results and being able to need some very very big maps, suppose you could make a map so massivly huge if you could by-pass the max limit... Wouldn't that lag a lot? or no?

If you need to have large sub-maps, then yes, the big map will end up being even larger.

the x-tra editor let you go to double the size of the normal maximum

But still, your limited to one tileset with only being able to re-place icons if your using the custom tileset option, not add additional ones.