I need similar functionality for my current project, including defaults for attributes. It's on my todo list -- What I'm working on will be for 6.x-2.

Hopefully I'll have something done soon, as it's pretty important to my currect project, and the entire project is WAY behind schedule.
(That means I'm working extra long hours to TRY to get everything done before the unrealistic deadline, which won't happen.)

Anyway, I'll submit it as a contrib and post a link here when it's completed. FYI -- Initially it may be feature lacking as I have to focus strictly on the functionality I need for my project.