The first and foremost goal is the absolute requirement that Pod be sufficient for easily writing text documentation, and that as a format it be simple enough that all its constructs be easily translatable into any sane markup language or typesetting system. I think that with new perlpod and perlpodspec and my forthcoming new Pod parser, that is pretty much taken care of. (Then there's just the cleanup work of actually bringing the formatters up to date, notably the currently appalling pod2html.)
The second goal is that Pod be extensible enough that you could use it as a sort of "Huffman-coding for XML" (as I remember Larry once expressing the idea, altho I'm quoting from memory, as I can't now find the exact message). This idea isn't a real requirement, but hooboy, it'd be nice if I could pull it off. I sort of have a working idea that fulfills a big part of this goal. Now I'm kicking around ideas that could get better coverage of the goal. It's tricky.