I wouldn't doubt that RHCP is lost to Activision but I think that there's a good chance that Journey and Soundgarden are being redone with the new system. The former would benefit greatly from keys and the latter would be MUCH better with harmony. Singing Spoonman was such a pain due to having to cut off one part to sing another. Likewise, Blackhole Sun has some great harmony that is sorely missing from the RB1 version. I really hope that we get updated versions of all of those songs. Like others have suggested, there is no point in them paying for the license to the old version when they can pay to relicense and remaster them to release them as paid DLC. I would gladly pay for updated versions of all 3 songs.
The only reasons I don't see this as the case with RHCP are because they dont appear to have a great benefit from harmonies (especially Give It Away) and because RHCP had a large enough catalog to warrant a standalone GH game, whereas neither Journey nor Soundgarden do. The ACDC stuff is probably just too expensive to license again without significantly raising the price, while Metallica is obvious. Finally, I expect the reason that the HMX songs are coming separately is because they will have keys, harmony, and/or pro modes included.
Anyway, here's hoping that GH finally goes away so that we can be free from stupid exclusivity agreements. To be fair, I don't like that RB does it either, but at least it prevents GH from reaching a similar deal.