You can but there are issues with having wmo's being that huge. Though right now I'm laughing like a hysterical maniac because I just did something related to your thoughts. Anyway before I get into that, if you make WMOs too big, like ADT Big, complications can and will occur, such as texture mappings will get rendered wrongly as shown in video below. Other things are, if you face a particular direction and are way out from the wmo's origin spawn point, the wmo will disappear from view.
Anyway about the texture mapping, you'll notice on the top of my HUGE object that the textures get screwed to hell.
Also some notes from my description on that video:
it's got around 800,000 polygons. WMO's can only have like 80k-90k polygons at most on WoTLK. So to get this sucker to spawn, I had to separate it into 10 separate wmo's. They are all spawned in the same place naturally.
Some parts of it seems like the texture is broken, it's most likely due to the scale of it since I had it at a smaller scale prior and the mapping was fine. Also each WMO Group can only have up to about 19,500 triangular polygons on them, so if you go over this, that particular group won't render out, and the total again is around 80-90k, too lazy to test for the exact number, too timeconsuming. There are your limitations.
Tools I used were blender 2.69 and this thing:
http://modcraft.superparanoid.de/viewtopic.php?f=59&t=3898
Though the texture screw up is mostly due to the fact that the Tool wasn't made for this sort of stuff. If I make the saucer a smaller scale, it doesn't screw up the texture rendering.
