Me and lots of others riders use indoor training systems very randomly, we prefer outdoor activities, but sometimes special in winter outdoor is not an option.
So Zwift must have a subscription type for this type of users/riders, for example have a subscription based on kilometers ride, for example sell a 1000km pack that will available untill you ride all 1000k independent of how long it takes, can be 1 week or 1 year.
Nope, pay monthly is the only option.
What you’ve suggested has been requested previously.
1000km behind a pacer isn’t the same as 1000km doing the Alpe.
I just stop my subscription over the Summer.
It doesn’t seem like Zwift wants to do that, but there are competing products you can try. Some are completely free, some offer a free trial period that might suit your needs, and some offer a free tier of service that isn’t limited by distance.