It looks as if you (Will) are trying to make some sort of equivalence between the idea of "going meta" and the "principle of sufficient reason", but surely these are completely different things.
Going meta (in the sense used here): saying "OK, so is there a reason why this is the way it is, and if so what's the reason?"
Principle of sufficient reason: "Everything that is true is true because of some prior reason sufficient to make it true."
PSR is not at all the same thing as "going meta"; it's not even the same kind of thing as "going meta"; it is one particular opinion about what sort of answers one will get when one goes meta.
It doesn't seem to me that the PSR is credible enough to warrant the sort of amount of attention you're trying to give it here, and in particular tying it to LWers' fondness for meta-ness seems entirely out of order.
(It feels to me as if the nearest thing to the PSR in LW tradition is not the idea of "going meta" but the idea of Solomonoff induction. But I haven't thought this through very hard.)
One of the sharpest and most important tools in the LessWrong cognitive toolkit is the idea of going meta, also called seeking whence or jumping out of the system, all terms crafted by Douglas Hofstadter. Though popularized by Hofstadter and repeatedly emphasized by Eliezer in posts like "Lost Purposes" and "Taboo Your Words", Wikipedia indicates that similar ideas have been around in philosophy since at least Anaximander in the form of the Principle of Sufficient Reason (PSR). I think it'd be only appropriate to seek whence this idea of seeking whence, taking a history of ideas perspective. I'd also like analyses of where the theme shows up and why it's appealing and so on, since again it seems pretty important to LessWrong epistemology. Topics that I'd like to see discussed are: