This is happened anyway, and they are capturing none of this possible revenue. Even if only one person purchased the early access and leaked it to everyone else they'd still be one sale better off than they currently are.
Yes this has now happened one time. It doesn't happen every season. If you allowed early release of episodes to customers who were willing to pay more, you can pretty much guarantee that those will be leaked early every single time.
I don't mean they should charge $10 or $20 for early access. I think they should be charging a couple hundred dollars - think VIP bottle service prices. Human nature being what it is, I suspect that people who are willing to pay for that level of access won't want to share it with the rest of us proles.
It works. Take, for example, $1,600 Photoshop Extended, which has never been pirated.