I was able to check out the 788T at NAB, and it is a sweet looking recorder.
I was told that future firmware updates would allow for recording of sample rates higher than 48khz, so for those that are concerned about that, it shouldn't be an issue for too long.
One new feature that I thought was cool was the LCD screen turns red when you are recording, and turns green when you are playing back audio. If you thought the 7xx recorders looked like Christmas trees before, wait until you see the 788T.
The recorder still uses the same Sony style lithium batteries as before, so you won't have to buy all new batteries if you plan on upgrading.
I was also told that the preamps in the 788T are actually quieter than the preamps in any of the other 7xx recorders. I haven't compared the specs myself to confirm this.
-John