Hello!
Is there some authoritative forum thread with speculations on future features or do the Authors keep a lid on this subject?
X.
In my experience, and with the occasional exception, GPSoft tend not to talk about new features/versions until they're ready.
It would spoil the surprise, if GPSoftware tipped their hand to early! 
Occasionally (or perhaps rarely), Greg or Jon will discuss a possible new feature in the context of a thread, but these are mostly to improve an existing feature or to correct an issue. Directory Opus has had the most improvement, version-to-version, over any other software that I have seen. Many of the new features have actually come from user-base submissions.
If you are looking for a particular new feature, you should submit a feature request to the official GPSoftware support site. I would suggest sending a detailed explanation of how the feature should work, along with a reasonable justification for the feature (i.e. how it pertains to more efficient file management in a real-world situation).