I wonder if this is the main issue:
‘Also, if you go in an Edit the template task with a new sub-task or something, it will automatically update all tasks that are based on that template with the new sub-task.’
I know there have been other threads that have requested this functionality before: (Push project template updates to existing projects, for example) and @Bastien_Siebman, you’ve commented on why that would be incredibly difficult. I have to agree. I don’t see how an update to all existing projects based on that template could feasibly work. There are just too many variables.