The revision (if they make one) would be smaller, without the GBA port, but with all the GBA port expansions built in: rumble pack, 32 MB additional RAM, tilt sensor...
But the next generation portable console should be cool indeed.
The next generation DS (or Gameboy) will have 8 GB of built-in flash memory. Games will be coded to the MAC address, so that they can be played only on your DS, and can't be copied. You will go to the store, pay for the game, plug the new DS into the game dispenser, and presto: new game. The true download play. This would remove the need for cartriges, thus greatly reducing game prices (for the developers; for us common folk, the prices will just drop slightly). This would also allow games to have more game save slots, (or, you would finally be able to have more than three custom maps in Advance Wars DS). Also, the device could be much thinner without the cartrige port. The GBA port will be abandoned.
Also, a tilt sensor, built-in rumble pack, Bluetooth, and a host of Bluetooth peripherals including, but not limited to, a Web camera, handsfree headset, GPS, external flash drive, etc. etc., sold separately for tons of $$$.
Both screens will be larger, of course, with better resolution.
There is also a possibility that the D-pad and other keys will be replaced entirely with parts of the touch screen (multitouch option, of course), making it look like something out of Star Trek.
...aaaand since I'm dreaming, I'd like a pony.
There. My suggestions. Discuss.