I'd like to take a step back and ask two questions:
What do end users want from a 'Theme System'?
Probably divided into at least two major camps:
What components make up a 'Theme System'
Well you have your oft quoted twins: 'Presentation Layer' and 'Content'
In PN most of the dynamic content is derived from the 'blocks' system with the static content derived from the theme code.
Unfortunately, the presentation layer is also partially dictated by the block system, with the theme code struggling to beat it into place.
So what am I trying to say? PN has a lot of legacy structure imposed on it. It's basis was designed and built by one person, based on that one person's needs and ideas.
We need to take a fresh look at the functional requirements of our 'Theme System' and document them before doing any coding.
The PN WIKI seems the most obvious place to solicit end user requirements - an 'RFC' approach...
BTW: Has anyone (been?) volunteered/earmarked to take the lead on the 0.8/theme project? - I do not have the capacity to do this role, but I'd like to actively support/assist the person who does.