A lot of people talk about the fact that once RingCT is implemented multisig will be possible, but it seems to be a very open statement, can someone give a more comprehensive breakdown of what kind of multisig use cases will be possible initially, as well as the limitations, upper limits and plans for expanding on multisig once it's initially rolled out?
Multisig will not be directly available once RingCT is merged. It will need further changes, which will build upon the RingtCT work. It is intended to allow typical N of M threshold signatures, in a way that is not visible from the blockchain (ie, you can't tell whether a transaction was made with multisig, or not).
See https://web.archive.org/web/20161023005318/https://shnoe.wordpress.com/2016/03/22/ring-multisignature/ for a description by Shen Noether, the author of RingCT.