Why is that a feature anyone would want?
You do not even need an account on Itch to buy games here. You can only follow, if you have an account.
And why would anyone follow you to begin with, if they can not see your project.
Maybe you are talking about something else. You have a patreon. There is some options to make files accessible to patreon followers.
Ok. Looks like an artificial method to inflate follower count. Itch does not like metric manipulations. Even if you do not intend it that way. It is unlikely that they have or will implement any gate keeping mechanism (except payment for paid content).
As I said, you do not even need an account to buy things on Itch. So even if you would sell something exclusively on Itch, people would neither need to follow you, nor have an account to buy it.
There is a mechanism to bother your customers with an email. But that is for paying customers, not for followers.
There is an incentive mechanism to have people pay more than 0. Put an individually priced file with price 1 on the project. The people that have paid can be rewarded in several ways.
But being a follower as a prerequisite? The reward of being a follower is getting notified in https://itch.io/my-feed about your public activities. It will be mostly your followers and the three people accidentally reading it in https://itch.io/feed and some few that might stumble on it with google. Talking about a changing password to your exclusive content in such a notification would make it kinda exclusive to your followers.
Interesting. If you are able to make it so only followers would see it and nobody else, how would it inflate follower count? My original intention is the opposite, to not get followers. Patreon allows pausing your account to not get new subscribers. Twitter allows private accounts, again to stop getting followers. Both could be set indefinitely.
Also, it isn’t for sale, it’s to be given for free to followers.
how would it inflate follower count
If you make something exclusive behind a prerequisite, that prerequisite is obviously needed to get the exclusive thing. For paid content, that prerequisite is the payment.
For free content, the cost would be giving the developer your user name and to get the developer's activites in your feed, which can be seen as subscribing to a newsletter. And the gain for the developer would be visible popularity. The follower counter.
On a site like GameJolt you can directly see how they value this. They only allow new developers that have a follower count of 1000+ on social media.
So to answer the question: it would inflate follower count, because people would have an incentive to follow. Without being a follower, you cannot get the content.
Patreon introduced something like that. Previously, any "follower" would be people that subscribed, and that included payment. But since a while ago, you can subscribe to a creator and the creator can make posts that are "free", but exclusive to subscribers. Having more subscribers, even free ones, makes a creator look more popular. But you still subscribe to the mailing list, in other words, you agree to get advertisement from the creator.
Anyway, as I said before, you do not even need to have an account to use Itch. Using the follower mechanic for any kind of mechanic for distribution does not fit in with that design.
It is practically certain, that you have silent followers. People that put your game in a bookmark. Or a private Itch collection. And probably some people that gave you money on Itch, but do not have an Itch account and cannot follow.
If you just wish to quietly give your followers content, but not block non-followers, just use a devlog or even a regular update. Your followers will get a notification. You could make an unlisted project and link to it from a devlog. But blocking non-followers is not something that Itch has any easy mechanics for, except payment.
