I'm afraid the problem is not solved.
Like David wrote, it is possible to subscribe to the contribution details of an extension in the database. This notifies me when new revisions come out.
However, the tab for Discussion/Support is not subscribed by subscribing to the contribution details.
I do not receive any notification when new posts are made in this section.
The same is true for Customisation Database - All support topics
I was not able to find any mechanism to get notifications in this important area.
I support the position that phpBB core should remain slim and extensions should provide additional non trivial functionality. This means that posts regarding extensions in the CBD are vital informations and are important to many of phpBB admins.
If there is a better place somewhere to discuss this issue, please let me know.