I would be cautious of looking to Overcast’s subscriptions as the reference model, since it failed a year later: https://marco.org/2016/09/09/overcast-ads
Instead, a better reference model I would look to (and that I’ve admired) is Plex. The base app was always free, but early on they introduced a subscription model called Plex Pass which at first did what you are suggesting:
- Gave access to the latest beta features
- Gave users a Plex Pass badge on forums to show off
Over time, their Plex Pass grew in value as they introduced premium features like sync to mobile. The strategy has been to keep refining the base features, while adding to the pool of premium features that made a subscription more and more attractive. Plex Pass has been a hugely lucrative strategy for what started as a bunch of coders creating a fork the open source project XBMC. They’ve since hired a huge team, and are supporting numerous platforms with quality apps.
Whether that model can translate to your app is not for me to know. But, I’ve always wondered why more apps don’t take this route of: pay once for the base app, a year later pay for the progressively increasing value of a subscription.