If a Event Registration has a number entered for Maximum Registrants, it would be great to have an option to show on the Public Registration Page and also possibly on the Public Calendar Page how many spots are left in that registration. 

This would help users know when spots are filling up and which events need more participants. 

This option could be an option as a checkbox on each specific registration page next to Maximum Registrants as users would likely only want to show this info for certain events.