Given our constraints, I think this is actually desirable.
However there’s a bit of a missing piece here in “leave it up to the person…to ensure enough people have confirmed”. The problem is that this question is already being asked on Talk, and people don’t reply. (Often because (a) some people get too much Talk traffic and (b) some people are rarely on Talk).
(For example I myself rarely check my availability based on a talk message, but I always do when Jamie sends me a skype message.)
It sounds a bit like we’re asking the proposer of a topic to use their personal connections to get people to share their schedules, and they won’t necessarily have those connections.
Can we help this by letting people share their skype/telegram/email contacts for this purpose? (I guess we’d make them available to people who are trying to schedule discussions, but not have these contacts be fully public.)