The only truly "vanilla" versions (not a lot of carrier/phone manuf. specific stuff) of Android for the D2 would be built from ASOP (Android source), like the CyanogenMod ROMs that are developed for a fair number of Android phones (see them listed here in the top of the wiki -
CyanogenMod Wiki).
A dev named Slayher is working on building a CM ROM from source for the D2...so hopefully we'll have that option in the near future. He's gotten it to load but not boot and it trying to get logs off the phone to find out where he's hitting a problem.
The other type of vanilla ROM would be a released D2 ROM version that was scrubbed by someone to remove as much of the non-Google stuff in it as possible (e.g., Blur) so it was more like a pure Google experience like the D1.
Regardless of the type of ROM, we won't be able to load new kernels w/the ROM to enable over-clocking the CPU until the bootloader encryption is cracked, but since the Drois is already 1GHz, it's not like we have a slow phone or anything.