The specifications for the rewrite should be complete now:
Let me know how/where you prefer to procede and discuss me, I'll follow
As for IRC, I'm Nemo_bis everywhere; we have a #wikiteam channel on
EFNet (not super-useful), I'm on #wikimedia and related on FreeNode etc.
Are you sure that PWB has all possible fallbacks? I thought some of them
were removed at some point. Moreover, by downloading a few thousands
different wikis in the wild I can tell you there are some very tricky one...