Malte, this is a great idea! It is similar to acs-rels, except that it is scheduling specific. Perhaps we should call it acs-schedule?
I think this is a really important item for dotWRK -- we can't compute how long a project will take to accomplish if we don't keep track of people's schedules, for example.
It looks pretty simple to code. I think we should probably make this a small package of its own. It seems like a candidate for inclusion in the core, but I guess that's not my call.
acs-events doesn't handle any of this, does it?