I like how they say 'the next one (update) will be a major evolution' those are big words to throw around so that combined with 'we are saving the best for last' (the second part of the announcement).....makes me think it truly has to be something big.....evolution implies a new or improved modus operandi does it not?
Here are my top speculations that make the most sense....
1. Multi-Rom----they have a gui so multi-rom isn't going to be that big of a next step
2. The ablility to run unsigned or modified Roms/code.....this would be good because the next step would be Rom hacking which would be huge for things like save game redirection (fixing the NAND save issues), defeating AP checks and patching boot executatbles to work on 4.5.
3. A real team patching system....like prometheus loader for psp which would decrypt and patch newer games at launch so they could run on older firmware.
4. 5.x/6.x support or even upgrade/downgrade support....what if they have found a way to read/write the Nand from DS mode...that way you could update and then downgrade again...that seems like a long shot but hey we are just dreaming here.
I like the use of the 'evolution' and in reality Gateway has been careful and conservative about what they have promised and have delivered what they have promisied so I think this will be big....Pokemon has surely already gone gold and gone to manufacture so whatever they release Nintendo won't have time to counter until the next batch of games (Zelda).
Even if it turns out to be multi-rom, or anything "less surprising" according to you, it's a great achievement, considering it's coming from a company that earned 0 trust from people before they actually used the product.