Personally, I think two separate things are called for. 1) A straight-forward update to use AES 2) Some public key system.
The p9sk1 *model* is great, and it'd be a real shame to drop it. Doing the upgrade and teaching should be easy, although there's tedious work in telling all the things to start using it, The fun/interesting parts live in that second one, though. Lots of questions, starting with deciding if something existing might make sense to import (Inferno's public key system is the obvious first thing to look at there, but its details are dusty in my head). Public key systems have different enough properties that it'd be good to have both, in cases where one or the other fits the use case better.
