I posted this in the TE board "What's allowed" thread, but haven't received a response. Has there been any decision on what degree of customization will be allowed for MA terrains under the new system? Will it be restricted to new terrain tiles, or will things be opened up more with custom objects?
Unless there is a very very large compelling reason to have a custom object it would not be alowed. And even then if the reason was so compelling we would add it to the standard shapes.
So the answer to you question is most likely no.
Also the tile sets do not add to terrain size, but rather the size of the main game download.
HiTech