None that I know of.
The HD2 lacks a front camera IMHO, internal storage memory too (not the TMOUS version, but the 3G frequencies don't match the European needs unfortunately) and its processor's speed will look outdated sooner or later as compared to more recent devices, but all in all, it stays the best pocket PC ever having been designed, and yes, it's the only one to allow so many OSes swapping.
It may be both because of not being locked by the maker, and because a lot of people worked on the possibility to port other systems...
Anyway, it remains the only one up to now.
It may also have something to do with the fact that Windows Mobile users have always been people curious to experiment with their phones, while nowadays, WP7 users will just buy a WP7 device, and so on for Android, I don't know. Remember Windows Mobile seems not to have been so popular in the past, though having been a real pioneer, far, far before the iPhone was even a project, and it did gain some real fans, that were generally from a generation where a computer was used to program and experiment with (just have a look to my nickname
It looks like some time has passed since then, and smartphones changed status, from swiss knife-like tools, to consumer products, thanks to makers and software editors policies, and thanks too to people changing phones twice a months.
I personnaly won't change mine for an empire, and I'm not ready to drop WM6.5.x. I bought several used HD2s from eBay, and if you really intend to keep the possibility to swap operating systems, you should do the same.
Otherwise, just buy a recent WP7 device : you'll still be able to upgrade anyway, as long as you keep up using WP7 of course.