It would be extremely useful to have a "cut off date" field in subscription plans. It would work the same way it works in Events Booking extension, as a way to set a date for a subscription plan to stop accepting registrations.
It's a must-have, especially for subscription plans regarding one-time events (eg. workshops). Right now, registration for a subscription plan is allowed even after its' Expired Date, which doesn't make any sense.
Please consider it for a future release of Membership Pro.
Honestly, this is something we won't add support for due to how Membership Pro works.
Usually, users subscribe for the plan, and then when subscription expired, they will need to renew their subscription to continue becoming active member, so limit the time they can sign up is quite useless.
I understand your use case, but for that, better use an event registration extension like Events Booking
Fixed date mean all subscriptions of that plan will be expired on that same date, does not depend on the date users sign up
For example, you might want that all subscriptions of your plan will be expired on 31 December every year, not depend on the date they sign up or renew their subscription. That's the usage of plan with fixed expiration date