yea I understand the compat issue with Xephyr ...
and boy o ...that is really really too bad the scratchbox-less build enviro was brick-walled. Hm...

And...when you said .."Continuing on this thought, suppose we had a cross compiler, and corresponding library development packages for a GUI toolkit (I like gtkmm on Diablo, qt on Fremantle). Using the same versions and build flags as used by the real maemo libs, so anything built with this toolchain could be installed on maemo with no additional dependencies...."
Hell I'm partial to that ..

and lastly ..."Hmm, I reckon you'd also want a way to create Diablo/Fremantle compatible debs, which would be another challenge."
yea ... hm..well for the time being at least..considering that fremantle has plenty of hands in the pot over all the n900debian, fptf, etc...I think there are enough brains pointed at those probs without adding to them immediately...not to mention..there aren't alot of current brains focusing on the n8x0 line...fact is...for a long time there hasn't been....the last couple months it's been pretty much just you and Kotczarny that have been doing the pioneering for the n8x0.
in the long haul it would be advantageous to have 1 cohesive method across platforms..but right now with all the n900 projects going on I think ..it better to wait on that idea. But for goodness sake don't you dare stop on the n8x0's!