Branch protection is also available in the open source GitLab CE. We made git-annex an enterprise feature because it is one of the few things that came up more from larger organizations, smaller ones tend to use a shared Dropbox.
More generally, I am curious how many of the "larger organizations" to which you refer in this context (clients interested in git-annex) are in the games industry, and how seriously interested your company is in trying to cater to that industry's needs? (Lots of game engines enjoy built-in first class support for Perforce due to how established it is in that vertical.)