Jetpack has opened a signup for the beta of its upcoming Membership feature in order to collect feedback from potential testers. The changelog for version 7.3, released two weeks ago, hinted at a new Membership block coming to the plugin. The work in progress was added behind the JETPACK_BETA_BLOCKS constant, presumably in preparation for wider testing.
Based on the feature’s description on GitHub, the first iteration will function like a recurring payment/donation button that uses Stripe as the payment gateway. In this case, “membership” might be a misnomer for the feature. The wording on the beta signup page lends to the confusion: “WordPress.com is currently preparing a feature that will let you enable subscriptions on your site.”
At the moment, it appears that the Jetpack team hasn’t fully decided what this feature will become and seems open to seeing where it will go. Beta testers will likely refine the direction of the block. If you have an interest in using Jetpack’s membership capabilities in the future and want to shape its development, you can sign up for the beta by providing your WordPress.com login and a description of your needs and expectations for the feature.