I do not know the answer to your question. I have a desire for friendly URLs, but have never spent the time needed to implement it.
But your specific issue of "how do we eliminate the fact that multiple page-specific lists exist for the same discussion thread" makes me wonder what the effect of senky's "infinite scrolling" extension would be in this scenario. (https://github.com/senky/infinitescroll
, now redirected to sitesplat.com)
I'm not sure whether that actually drops the pagination parameter or not. But it makes sense that "it could", since all the posts for a given thread are now "on a single page". I also do not know, but assume, that it achieves the same thing for the list of threads within a forum.