I like the idea of using a Host entry and then being able to either choose a sub connection to launch or select templates. Could these features be somewhat combined?
1) Sub connections could be added to the host that are based on a template (the same was as the Action>Choose template option works)
2) One of those sub connections could be selected as the default action.
Thus when clicking on the host and selecting open session it opens the 'default' sub connection, but the other sub connections could be accessed from the tree view if needed. If purely using the Action>Choose template option it means that you have to select the template to use each time (if you have multiple) even if you only occasionally need to use one of the other templates and its also not possible to just select the template you want to connect with directly from the tree.
Also as a semi related item, it would be good to create sub-connections based on templates even if the above isn't possible.
I have added a feature request to add this. I will keep you informed of our progress. I'm not sure if we will have the time to do it for RDM 12.