I am missing this too from the Garnet VM. Assuming the VM behaves like a normal OS5 device (allowing arm hacks, slot libraries...) a PalmOS slot/filesystem driver could be written that accessed a Maemo-exported filesystem (or even a single folder) using the loopback network connection, which seems available to the VM. Not so fast as a native VM exit, but quite good I think.

Advantages over RAMDrive: NIT's SD Card can be mounted/exported to PalmOS. Easy(ier) file sharing between Maemo & POS.
Advantages over hypothetical "GVM Beta 4" with SDCard Support: Right now I don't believe GVM will get another upgrade anytime soon...
Disadvantages: documentation for OS5 slot/filesystem driver probably missing/outdated.

(BTW, first post -- just bought a used N810, already enjoying it -- I used to be a Palm fanboy, but my T|X broke, and I dislike Palm,Inc. newer devices).