Where did Chrome enhanced bookmark manager disappear?
Solution 1:
As far as I remember, Google has been regularly deleted this extension from Chrome Webstore.
I'm using it right now - I never delete extensions, only disable them and if I check details it gives me this link - https://chrome.google.com/webstore/detail/gmlllbghnfkpflemihljekbapjopfjik
Keep in mind, that Bookmark manager is still in development phase.
Edit: If you really want it, I can make a copy of extension.
Solution 2:
Apparently Google finally decided to revert to the old bookmarks manager - see here.
You can now get the enhanced bookmark manager as an extension from here.
Solution 3:
I found the problem and the solution (at least for my specific case).
I believe Google (accidentally?) disabled the enhanced bookmark manager (regardless of the chrome://flag setting) in the Chrome dev channel, which is the one I've been using (version 43.x).
I uninstalled Chrome and installed Chrome stable channel (the default), so I'm back to version 41.0.2272.118 now, and the enhanced bookmark manager is back, hurray!!!
Instructions on how to switch Chrome channels at: https://www.chromium.org/getting-involved/dev-channel
Note: it's was not enough to install the stable channel over the existing dev channel installation, since it does not downgrade the version - I had to uninstall first and then install again.