While the recent news about the DLC outage finally ending for all users, it looks like another form of Rock Band may be coming to a more permanent end in the near future. Rock Band iOS app will “no longer be playable” after May 31st, according to an in-game pop up message when loading the app (see below).
Despite the impending fate of the app, there are no indications that a similar situation will be occurring with the more recent Rock Band Reloaded app.
They probably ran out of licensing time for some of the songs and had to disabled the app. This sucks hard though.