It would be useful to be able to "freeze" a release, ie to put it in a state where no new issues can be assigned to a release (when discussing with a client, they tend to agree on a number of features/fixes to put in the next release, then over time they want to add and add and add... making the release overflow with issues (if the release date has been set)). The best would be that jira prevents adding issues, but this is probably more involving. If it could at least show clearly on the release (version) pages and maybe when selecting the version when assigning, then it would already be a first step.