Yes, pimlico is available for the N810; the OS for N800 & N810 is identical (flashed from the same firmware image). Software issues generally are the other way around: some software "works" on both, but is only useful on the N810, because it needs a keyboard. AFAIK, pimlico is cool on both. (I don't use it.)

WRT multi-boot; I'm running a quad-boot right now... OS2008 on the internal flash; OS2008 (with stuff grabbed from the SDK to build software), pre-release Diablo (an upcoming release we ganked off an unguarded repo; the release is due "in second quarter of 2008".), and Debian Lenny on the SD. And I still haven't touched KDE... not that I plan to. While it's cool, the lower-spec WMs are more practical. I intend to build fvwm2 when I get time.

If that's the kind of stuff that trips your trigger, buy it! But don't toss your Zire yet; even the available PIMs (pimlico and GPE) are said to be rather below Palm's level, and a number of users keep a Palm just for PIM. I don't use any PIM, so I don't know. Just saying...