They haven't abandoned it..... Some people poking around the site have found evidence that six songs are already earmarked to get pro upgrade at some point. It may or may not actually come to pass, but there's no reason to call 'abandoned!'.
I got an problem with Blitz related to this. I cannot find the free song pack to download in the Xbox Marketplace under this game. I already have downloaded Blitz yesterday but only see 3 songs in Blitz which isn't playable in RB3. Harmonix have better fix this so it would've told me after I ran the game the first time to download the free song pack.
The pack is not in the xbox marketplace, you should get a pop-up when opening blitz asking if you want to download the songs. Some are saying it takes a few tries of opening blitz but eventually you should get a window asking if you want to download the song pack.