It Seems IGN has some information about Rock Band 2.

Good news is you WILL be able to use your old DLC from Rock Band 1 in Rock Band 2, so that will calm alot of nerves on that front.

Now really, anyone who thought there would not be a Rock Band 2, considering who the publisher is, was fooling themselves.  However, I think this will be a good thing, as it seems they will be adding new features such as ONLINE band world tour (thank god) and possibly new peripherals?  One thing of note was the statement saying a guitarist and singer can be one in the same now, so no more creating 2 characters to do what you were possibly only doing yourself.