I am currently rooted but still on the stock MR1 radio/ROM. I rooted following the instructions at
[ROOT] MR1/OTA PermRoot + Unlock Bootloader - Safer/Easier 5/12/2011 - xda-developers
I would like to update my radio to MR2 (especially after having problems this weekend with indoor connectivity in some Long Island locations that have 4G). However, from everything I read, the MR2 radio requires an MR2 ROM (and won't work with the MR1 stock ROM that I'm currently running). I have not yet seen any instructions on how to upgrade the stock ROM to MR2 while rooted, nor have I seen a rooted stock MR2 ROM (only an unrooted MR2 stock ROM).
I'm not interested in installing any of the 3rd party ROMs that are currently out there. I plan to ultimately move to CyanogenMod which I previously ran on my Droid, but I'm waiting for it to progress to a more stable state (preferably "gold' release, but I might jump to it when it gets to a release candidate state if that looks stable/complete enough to me).