There's one good reason to not support a very high resolution in the next iPad model:
Fragmentation.
For such high resolution, apple will likely increase the RAM to > 1GB (which is not an issue) + a very fast processor.
The main problem isn't this configuration. The main problem is that the first iPad shipped with a slightly lower configuration and therefore a big bump might create a visible fragmentation which apple wouldn't want.
So I guess, they would go slowly and keep the backwards compatibility for atleast a couple of years.
BUT:
If the iPad doesn't sport 512MB RAM and a very fast processor, it will again be on the side of a lower configuration spec and Apple wouldn't want that as of now.
So its really a design decision:
Does apple wish for apparent fragmentation (likely possible) in the coming 6-8 months of the product?
OR
Would apple want to be agressive and keep their products up to date.
Also, the "visible fragmentation" won't be visible until 4-8 months of the product but still will be a huge concern for apple.
PS: Avoid grammar and spelling mistakes; I'm in my office.
Cheers