I'm pretty sure you're going to see a new receiver (HR24?) to go with the new tivo software, and there wont be any options to field upgrade an existing HR2x from the directv software to the tivo software.
As far as how much of the tivo software will be in it (mrv, tivo2go, netflix, etc) remains to be seen. If they hobble all the extra goodies like they did on the directivo, then its practically worthless as far as I'm concerned.
I'm also quite sure you'll have to ante up $200-250+ to get the new tivo box, send your old 'leased' box back in, and pay more than a $5 a month per account dvr fee. My guess is ~$6-8 per tivo box per month.
My contract with directv is up in April. If the directv dvr box isnt fully stable, have mrv and a responsive remote control by then, I'm just going to buy a couple of tivo HD's with lifetime service and add digital cable. I'm already getting cable internet, and with the combo deals I can get full digital HD cable with the internet for not much more than i'm paying for directv alone. So it'll be cheaper, more reliable, have the features I want, and comcast has every HD channel that I watch. Not much downside.
Then the only thing that can screw me up is if Comcast sticks the 'do not copy' bit on every show, which will prevent the tivo mrv from working. I guess thats a big problem with some cable providers in some areas.