Please consider adding SD2IEC emulation. The native file system emulation does not provide a couple of key areas of compatibility that non-trivial uses of VICE requires:
1) REL file support. SD2IEC does this in native folders.
2) Partitions support. SD2IEC does this on any device that is hooked up, including SD-Cards
3) Real Time Clock support. Though not implemented on any CURRENT SD2IEC design, the firmware supports RTC access via the CMD standard. Software that supports the CMD clock standard (such as GEOS) would benefit from this availability.
Please don't just dismiss these issues as non-issues. There are many things that programmers want to test that are available on many large devices, such as partitions and REL files, that simply cannot be debugged and replicated in VICE today.
You can find the hardware specs at: http://www.c64-wiki.com/index.php/SD2IEC#Weblinks
You can find the firmware specs at: http://www.c64-wiki.com/index.php/sd2iec_%28firmware%29