I know that the plus 4 and C16 are closely related, but are they so closely related that there's no point in an emulator for the 16? Ive not seen one included with VICE.
The C16 is the same as a Plus/4 but with only 16KB of RAM and no 3+1 software. Just go to the Plus4 settings in VICE and reduce the memory to 16K and you have a C16 :)