The thing is, I am really far from sure such mod would help out in any way.
For sure, we can see many boards using such mod but, for the reasons I started to elaborate here
, I don't think it is this good.
Because, event if the outputted code is not the same, you'll get almost the same txt content and page title and will create competition in between your pages.
so I'd say such mod are not necessary at all if you forum is spidered well enough, it's only useful if, for example, you do not SEO your forum, as those archive pages will be spidered easier in such case.
But, with mod rewrite and mx Google sitemaps
you'll most likely get fully spidered, so all you want is mx sitemaps
instead, which will provide links only and not content, helping you out to build up a stronger PageRank on the pages you are already working on (the topic, forums ...).
Remember mx Google sitemaps is able to output a really large amount of link (up to 50 000 actually) from one forum at once and that mx sitemaps can use different pagination settings than the boards, look at the way I set it up here, it's 25 topic per forum's page
on the forum and 40 on the sitemap
Enough to dig out old threads I'd say.