Time to drop the biggest effin'
If you follow the rumor and leaked news mill around MS and it's products then you all should know MS nerd and his/her record to date which as far as I remember has been spot on.
Then, going by the above tweet, it would seem MS and Nokia are testing WP8 on the low, very low, end Lumia 610! If true this should bode well for upgrading first gen phones as well as offer us an idea of the type of performance MS is aiming for. If the other rumor about WP8 sharing it's core with Windows 8 are true then MS has done a load of performance and optimization work moving over the NT core to the phone. If something as low speced as the 610 can run WP8 well then the rest is just what features are or are not supported depending on the rest of the hardware?
Either way, this little tidbit, if true, should be a clue to the future support of WP8 on older devices. If MS wasn't going to support them then why even bother to test on such a slower phone like the 610 at all?