I'm not against sub-events but I would prefer something well-defined, robust and secure than having a bunch of new features not properly designed and integrated. Looking at the picture, it seems simple and easy to do. But then thinking about concept behind, I agree with Joshtek, it could easily become a mess and increase risk of programming errors due to specific language features to handle.
People aren't going to just be adding sub-events without first learning what they do... just like anything in the program.
Unfortunately, people uses everything without taking the time to learn and then complain on the forum because it's not working.