Noob question: what is a “workspace” in the sense that you’re referring to? Is it a user-facing concept? (I’ve seen it in the plugin API, but as far as I can tell there’s just the singleton workspace there.)
In any case, what you’re suggesting sounds like exactly the sort of feature I’m hoping for. (I recently posted about it here.) Presumably it would be easy to create a workspace from a folder.
EDIT: I did some digging and figured out how to enable the workspaces plugin. I’m not sure I 100% grok how workspaces are supposed to be used, but it does seem like tying a workspace to a set of “files I’m interested in” would be a sensible approach.