Allow new tiers to be set for an opening launch date!

This feature would allow you to create a tier(s) set to launch at specific dates. Maybe folks could even sign up for a notification to be sent on the launch day. Or pre-pay for this tier and be charged on launch day. Similar to a pledge on substack, a new invitee gets to see that this option is coming and sign up for it when they land on the tiered plan options.