We will not be doing a 4.6.4 release.
We're currently merging changes on the 4.6 branch (oacs-4-6) since the last merge (4-6-3-beta1) back onto HEAD.
Any new development, bug fixes, etc., should happen on HEAD from now on.
Heidelberg needs to launch late September, and we'll be accomodating the 5.0 release to their needs, so you can expect some form of release around that date.
More details on dates and release criteria in a separate thread, when we've had a chance to plan out the details.