My source of information comes in the form of Amy discussing this a few nights ago in game... (I don't have screenshots, but there were quite a few people in the room at the time) But she didn't really say much about releases except that if Music Mixer or HM arrives expect the other to come out not far after... She said that by the time the game releases to 1.0 we will have all of the games but POTC. Amy said a couple months ago the POTC is actually more difficult than HM and will be the last one released.
And fun fact about the Music Mixer for earning credits. It will be done in a voting system style to earn the credits. The more up votes you get for your music the more credits you will get. I hope it comes out soon, but I'm not entirely certain when it will be released. I'm not completely sure how ready it is...
Again she didn't really give any release dates for anything as she doesn't like to do that because something could cause a issue that she didn't expect. All the stuff I have mentioned is stuff I believe she is hoping to have finished by certain points in the game, but again some unexpected things could happen to cause delays. She may have more updated information if she wishes to share it or change anything I said. This is from my memory and I may have said something incorrectly, which I can do quite a bit >_< (and sorry if I did Amy :P)