Subscription For Clients (NOT PACKAGES)

I run a photography studio for hire, so rather than offering individual services I offer bookings of the space on an hourly rate. I want to be able to allow clients to subscribe to memberships so they can have a certain number of bookable hours per month, and get discounts on extras if they are subscribed. Like a membership rather than packages. For example if the client has 6 bookable hours on their subscription tier, they can book those 6 hours in whichever capacity they require eg 3 x 2 hour sessions, 2 x 3 hour sessions, a 4 and a 2 hour session. Hope this makes sense but it would be a hugely helpful feature I fel lik the main thing booking press is lacking is flexibility for businesses that aren't based solely around booking a specific service but rather a duration. Even offering documentation and allowing custom development would be great, that's something that would make customers feel like this is an elite booking system and the best for WordPress sadly we're just not there yet.