Ability to set a date to close RSVP

Example:  planning a ride on june 6, but I'd like to book hotel blocks at least a week in advance.  I'd like folks to RSVP no later than X date and close it to new RSVP on that date.

Waitlist ties into this.
We've got to figure out how this works with atprotocol.

Needs more detail before it's ready to take up. 