It should be possible to exclude some branches from being a job created at all.
e.g. we only merge to the master branch while we do a release, but there should never be a build triggered from the master branch itself. As a result we don't like the master branch to appear in the list of jobs at all.

I think an additional regex to define the branches to be included would be a perfect solution.

While there is an option in the "Bitbucket Team/Project" type to exclude jobs from automatically build (via "Automatic branch project triggering" of the "Branch API plugin"). This has not the same effect, a job is still created and a user could potentially trigger it in the UI.