For a compact Mac->VGA adapter, if you were going to make it a plug and play device, you'd need to pick a generation of compact Mac to start with.  The 128-Plus had one kind of connector from the LB to the AB, the SE-SE/30s had another, and the Classic & CII had the same as the SE only wired completely differently.  You might be able to make something with one connector and an SE/Classic switch...

I'd start with the SE/x family simply because you could make a nice plate to mount on the back.