The first wave of Gen 4, Sinnoh, Pokemon have now been released. From what I have caught, thus far, it appears that the first wave of releases consists of the starters, Piplup, Chimchar and Turtwig along with the normal and Bug type Sinnoh Pokemon. More waves are to follow, with the next wave most likely to include the dark and ghost types arriving in time for Halloween.
A further increase for the maximum Pokemon storage that can be bought from the store is not live yet, but has been announced as incoming by Niantic. So if you have already bought and filled up your storage space then panic not. There has also been a change in the gym bosses to reflect the release of the first wave of gen 4 Pokemon with the gym bosses now as follows:
Bidoof (Gen 4)
Buneary (Gen 4)
Kriketot (Gen 4)
Shinx (Gen 4)