@LibertyLocked on twitter
DLC will work in DC2 and should automatically work without needing to do anything short of re-downloading them if you had deleted them. The songs from the DC1 disc will require you to redeem the code from the manual and pay a fee to import them.
I'm not sure about the pay a fee part spinoff
Pay a fee for what i have already bought? doesn't make sense at all
The e-mail about the DLC on sale this week says at the bottom an extra fee will be required to export from DC. Will be the same as the Rock Band games. Disc export will have a fee to cover licenses (Unlike RB it seems they have managed to renew all songs) while DLC will automatically get detected without a fee.
?? Just have to wait and see.