When people ask me why I chose to embed Lua in my mail-client I'll point to my on_idle() documentation.
Moving from a callback which runs once every second, or so, to allowing the user to schedule tasks on arbitrary boundaries is pretty cool - and obviously requires no explicit support from myself.
Now I've fixed a couple of bugs which went unspotted/unreported in the first release I'm ready for a new one "soon".
In the meantime I'm running the client exclusively, and loving the ability to view all unread mail, only, regardless of the parent folder.