If you look in your Program Files (Win) or Applications (mac) folder, into the Poser default runtime there, where the addons are installed under runtime:Python:addons:dson...

...you'll see a Python file called init.py ...and that's about it for the uncompiled Python, by the looks of it... anything else in there looks to me like compiled Python or C++? (including the QTCore framework files)

I reckon all that possibly can be is probably already compiled?

So, if that's the case, then the bottlenecking is occuring... I'd guess... either due to single-threading where there needs to be some parallelism... or just down to a lot of iterating code that isn't fully optimised. But that's just a guess.

That "projection" stage, when I run it, fires up about twenty or so identical progress windows (all stacked up over the top of each other). They count up the execution time and disappear one by one, synchronously, until the process is complete.

At a guess, I think all those are probably meant to ideally be one dialogue, with asynchronous processing going on behind it? That's likely how the equivalent process runs in DS4.5... I'd suppose?

Anyway... unless any Poser Team or Daz devs are about to chip in now, I suspect we're in a pretty speculative realm here... I'm expecting just to sit back and wait for the next DSON Importer build and / or Poser 9 / 2012 Service Release 4... to see how well it can all be improved...