As someone who is rightfully frightened of breaking everything on engine updates, I think it’d be really sweet to be able to add 4.11 (random example) as a new version alongside 4.10, instead of only being able to update it via the launcher.
This is already an option. While hotfixes are version specific (for instance, 4.10.1 is a specific update to 4.10), each engine version is installed separately and do not overwrite one another.
You can already accomplish this level of control (separate Hotfix versions) by utilizing our source code builds via Github forks. You may find this to be the best option for you.