Hi James,
Thanks for taking the time to reach out! While we don’t yet offer this feature as a bundled feature or add-on for Event Tickets Plus, it seems like an idea that’s definitely worth exploring, perhaps for our Extension Library! Would you mind sharing your idea over on our UserVoice forum, where we collect feature suggestions from our user community? This will get your idea on the development team’s radar and will allow other users to share comments and vote their interest, as well!
https://tribe.uservoice.com/
In the meantime, this forum post may offer some ideas to get you started on a stopgap solution:
https://theeventscalendar.com/support/forums/topic/subscription-3/
I hope that helps to get you on your way here! 🙂 Thanks again, and let us know if you should have any other questions!