Is there a plan to support versions 4+ ?

[Steffen Opel _Utoolity_]

The feature offered by the Protect Branch Delete add-on is meanwhile available within Bitbucket Server itself, see Branch permissions:

Branch permissions:

• [...]
• prevent unauthorised users pushing to or deleting the branch.
• can be based on explicit branch names, branch pattern, or branching model.

Given that updating an add-on to Bitbucket Server (formerly Stash) versions >4.0.0 involves a significant investment due to the host product rename also affecting the internal API package namespace for example, I doubt that there are sufficient reasons and motivation to update a semantically obsolete free add-on and would recommend switching to the similar core product feature instead.