Basically during an edit I am often trimming dialogue audio where I want a ~5 frame default transition, but then adding crossfades to music where i usually want a ~20 frame transition. I am adding a lot right now!

Basically my suggestion is two default audio transition lengths, one being the primary default, and the other being a "secondary" default that could be activated by a different shortcut, maybe Ctrl+Shift+D (of course can be set to whatever you want).