Bluntly, I don't see any future in which all of the RBN 2.0 content is released on PS3.
It takes time and effort on both Harmonix's part and Sony's to bring an RBN song from Xbox 360 to PS3. This means that there's effectively a cost to bringing out a PS3 RBN song. If the song then doesn't sell above the threshold required to recoup that cost, then Harmonix and Sony have effectively lost money by bringing out that song. This is, unsurprisingly, something we wish to avoid.
By contrast, now that the RBN system exists (thanks to Microsoft's massive investment and incredible development at both Harmonix and Microsoft), we don't experience the same kind of production/development cost for songs to come out on Xbox 360. While I hate to be depressing, this means that Xbox will always have more RBN content than the PS3 will.
On the other hand, by nature, I think the cost/time of porting RBN songs to the PS3 is cheeper than charting entirely new songs, so it's possible it may continue well past any official DLC end date.