As far as I know, it hasn't been announced as ready yet. From what was posted by one or two MDPT devs, what it's going to be is a selection of stable libraries that MySpace will host, and that developers will be able to import into their JS without fear of having their Apps rejected.
There's probably a bit more to it -- it was mentioned somewhere here on the forums that the Guidelines are under-going some changes as well, to help developers in this area. Which is a good thing -- common UI components across Apps will make users more comfortable using them.