I feel like this is a major misstep for the framework and only gives people an reason to use something different.
Once you start using a real database with your project, which I bet most of us are, the restart times are unacceptable. I convinced my employer to get us JRebel but it's horribly overpriced for what it does - like 6x the cost of IntelliJ per person.
My org is starting to step into Django, which seems to hot swap perfectly fine out of the box, and it's like stepping into a time machine and going back 20 years compared to working with Grails. We are having a meeting to discuss how to structure the MVC'ness of the project, and with Grails that's a 2 minute discussion.
If I were starting over and staying in the Java ecosystem I'd probably just go directly with Spring Boot at this point.