This was initially discovered by developer Alessandro Paluzzi where he came across a message on Instagram Stories that hinted that a subscription feature could be in the works. What this does, assuming it is what we think it is, is that it would allow creators to lock content behind a subscription so that only those who are subscribed can see it.
https://twitter.com/alex193a/status/1406995654900125702
If this sounds familiar, it is because in concept, this is similar to Twitter’s Super Follower feature. However, it seems that this will only apply to Stories, which means that the creator’s photos and videos on their profile should still be visible to their followers. According to further digging, it seems that these exclusive Stories cannot be screenshotted, presumably to prevent people from sharing it with non-subscribers.
Since this seems to be something early in development, it’s hard to say what the company has planned for it or what it could look like fully fleshed out, so we’ll just have to wait and see.