so sir, do you think it is possible to do east frozen, south desert, west in that classic weather we have now and who knows, the tropical jungles in islands around the maps (those scenarios sounds familiar to you guys?
) with 12 textures or less? would the mappers comunity be up for the challenge? 
Also as for the final product, depending on the file size even if it is 12 textures, HTC could decline the map for usage?
Is it doable as you propose for the MA? No. Not with that many land use types and seasons. It would be difficult for any arena and once you start mixing ETO summer with ETO winter for instance, you're forced to start creating custom copies of objects, specifically all the trees, bushes, grass etc so that you can map your winter textures to them and still keep the summer versions.
That doesn't mean you must have all grass terrains of course, but it takes time to set 16,777,216 plots of land with up to two (blended) of the 12 land use types. Most builders are going spend that time setting spawn points and correct road layouts instead.
I spent many many hours working on the mountains in avasml using the default ETO set. The new terrain engine had just come out and I was experimenting. I think they came out looking pretty good, but it's a tiny terrain, not a massive 512x512 monster.