@ShawnHymel — I believe there does exist a method to unpublish the landing page the form is embedded on by a certain date. Many CMSs have the ability to unpublish pages after a certain date—HubSpot landing pages can do this too (or, if you prefer, revise the page by replacing the form with “This event is now closed” boilerplate, and then scheduling that revision to publish on a certain date.)
This certainly isn’t a solution to the basic problem (e.g., the only variable you can work with is date/time.) Hopefully you can use it as a patch until HubSpot develops more robust forms.