[Dovecot] mbox and dual-use folders?

Feature request: please can we have support for messages stored in mbox files, but folders containing both messages and folders. I think this could be done for a folder called e.g. dovecot-list by having an mbox file called dovecot-list and a directory called dovecot-list.folder (or whatever, says he handwaving away name clashes which can be worked around like they are in maildirs). This may be a subset or variant of http://wiki.dovecot.org/FeatMboxMaildir

Cheers,

John.