Addendum:

> the incompatibility of the e500v2 core is the reason the UltimatePPC has been
> put on hold (or cancelled?).

Interestingly, two years ago and more than one year after the UltimatePPC team announced they would eventually reconsider their choice of CPU, Trevor Dickinson reached out to them:

http://eab.abime.net/showpost.php?p=919823
http://eab.abime.net/showpost.php?p=919837

Any guesses what they talked about? :-)