Using is available for registration in access

I don't think it's particularly important, but thought the idea might be worth sharing.

Thanks @jonathanshaw. That solution sounds like something good for a custom module. The UX when running out of room is not ideal if you just remove the Register links, which access control does, because the removal is unexpected in this case. Typically the host entity page will show the event date, so there is no surprise when the link disappears when the event date is reached. But if the link disappears a week early because it was overbooked, people will be wondering what happened, why can't I register? Thus it is better to have the links still exist and let the register form explain with a message. Obviously some text could be added to the host entity page as well, but that may not be practical for sites with many hosts, or social media posts may have direct links to the register page - do not want those to get a 403 a week early. I suppose someone could setup a redirect, but again, not sure that is always practical.