I have now tried this, and it is amazing! Not in the sense of being, uh, "The computer environment I always wanted" (I haven't tried it long enough to have an opinion), but in the sense that it is a completely new computer, again. To me, who has never heard about RiscOS before, this is a complete new environment - And it is running native on my pandora!
This really is an embarassment of riches. Just by changing the left card, I can make my little computer run Ångström, Slackware, Android or RiscOS. All of these have different software ecologies and different environments, so that in a quite real sense, they make my pandora into 4 different computers (ok , 3½, given that Slack is also a linux). And that is before we've considered emulation at all.
To a retro-quirky enthusiast as myself, this is pure bliss. Thank you Raik, as well ass all the other developers who transform my pandora to new wondrous things.