Trunk based development fits well with well defined sprints and continuous integration but I'm not sure that not committing into a release branch is the best strategy when the releases are kept small and the development continues with full force after the release is formed. In my experience it makes sense to fix found bugs in the release branch and then merge them back - expectation is that these fixes are really minor as the release is not created before mainline development has been validated and is ready for the release. No new features should be added into the release branch, only bug fixes. In such case merging back small release branch changes has not proven to be any pain at all.