Oculus has announced on its blog and likely in your inbox the first (of many) supported Quest titles that will offer the ability to purchase premium subscription content.
Quest titles including vSpatial, FitXR (BoxVR), Tribe XR, VZfit, TRIPP, and Rec Room are the first Oculus Quest titles to support premium subscription content inside the app. The content that gets unlocked with your regular subscription varies between the app in question.
FitXR for example offers a 90-day free trial of its premium subscription membership, which allows daily instructor-guided workouts, multiplayer mode support, and HIIT studios for $9.99 per month.

The Rec Room Plus subscription offers members 6,000 monthly tokens, free 4-star items each week, access to its RR+ section of the store, 10% discounts in token stores, access to 100 saved outfit slots, and the ability to sell creations to players for tokens. All this is for $7.99 per month.
Mindfulness app TRIPP will offer a $4.99 per month subscription to receive daily focus and calm TRIPPs, compose your own TRIPPs, access 40+ mediative experiences, and personal your experiences, tracking and process in the TRIPP mobile app.
Most subscription content is a layer on top of the current offerings and all subscriptions are optional. Some of these apps, like Rec Room, are free to play and this is their way to keep producing new content for free members whilst offering premium content to paid memberships. Whilst other paid apps may offer premium subscription content to enhance or boost the functionality of the app and its content.

Before this reveal, Oculus and its apps on the Quest were using a familiar console model of pay once and you own the game, with DLC provided either free or as an additional one-off payment. Now, developers have the ability to offer a subscription model to either a free or paid game in order to earn extra revenue for their game and help create their game or app as a service.
A model of this kind is a solid step forward for developers looking to create in the VR space. It allows them to create freemium applications, very similar to models you may have encountered on mobile apps and games. Developers can also offer titles for free and give a hint at the game before signing up to a subscription service for extra/deeper content – that is a win/win for both player and developer in my eyes.