It's no longer necessary to use a custom dial plan under FreePBX 13 with core 13.0.5 and later though (unless you want to do custom stuff like playing the message in two languages like I do) as Andrew merged in my fix and published it...
It sure would be nice but I wonder who would use it...
It might be a little too complex to use for some people and the ones who would know how to use it would most likely be able to do it directly in custom files so I wonder if it would be worth the effort of doing it though...