I am sorry you’re struggling with this, and I’m sorry it feels like a burden to you. I hope you will do whatever you need to do to manage the stress and anxiety it is causing you. AO3commentoftheday and alexseanchai had some good suggestions.
But I do think you are so focused on what you think your subscribers expect of you that you are missing a few key things. As someone who has subscribed to a lot of people, here are my thoughts:
1) Some of the people who subscribe to you are probably polyfannish, that is, they read fic in a variety of fandoms. For all the ones who go “ugh, this isn’t what I followed them for!” there are others who will go “yay, they’re writing in this other fandom I love!” or “yay, a new fandom for me to explore!” (Seriously, I find new fandoms regularly because my favorite authors start writing in new fandoms, it is a joy.) The people who will be happy you’re writing in a new fandom are just as real as the ones who will be disappointed you are not writing exclusively for their fave any longer.
2) Subscribing is not a contract. This is not patreon, they’re not paying you in exchange for content. This is not social media, where people share content and interact in social and parasocial relationships. When someone follows you, you have no obligations to them whatsoever beyond the common obligations we have to each other on AO3 (don’t deliberately mistag your stuff, etc.). All subscription is, is them asking the archive to be notified when you have new content. There is no guarantee as to what sort of content it will be or how often it will come. If they like it, great! If it’s not their thing, that’s fine! The burden of managing subscriptions is completely, totally, and always on the suscriber’s shoulders. It is not on the creator’s shoulders. You have no obligations toward the people who have subscribed to you.
3) There is never a match of creator and subscriber so perfect that the subscriber will like every single fanwork the creator makes. There just isn’t! Even if you only ever posted in one fandom with one pairing, I guarantee you that every single person who subscribes to you would have some fics they love and others they are meh about and others they don’t like. That’s the nature of the beast. And even if, somehow, you could magically only produce works that all of your subscribers always like, they’re going to move on too! Most people get tired of a fandom eventually and move on. It happens! Your tastes and fandoms will change over time, and so will the tastes and fandoms of the people subscribed to you. And that is fine! That’s life! That is the way fandom works. Things change. You change, your audience changes. It’s natural and normal and good. The only possible result of worrying about “will my subscribers like this?” is making yourself crazy. There is no possible good that can come from that question.
4) If a subscriber doesn’t like a fanwork you create, the worst thing that happens is that they get an email notifying them of the existence of a story they don’t want to read. That’s it! That’s as bad as it gets! A single email, easily deleted. The absolute worst thing that can possibly happen is that someone looks at the email, takes a few seconds to decide “not my thing,” and hits the delete button. (Unless, of course, you’re deliberately mistagging things in an attempt to deceive people into reading your fic, but that is a problem on its own that has nothing to do with subscriptions.)
5) If a subscriber doesn’t like the sort of content you’re creating now, they can unsubscribe themselves. It’s very simple! There is a link at the bottom of every single update email to unsubscribe from the creator, fanwork, or series they subscribed to in order to get that notification. Or they can go to your profile page, and the unsubscribe button is right there at the top. And this is the subscriber’s choice to make. It is always within their power. If they don’t like being subscribed to you, they can stop at any time, and it is quick and easy to do so. The burden is on the subscriber’s shoulders, not the content creator’s shoulders.
6) If someone is mad that you’re creating in new fandoms, that’s their problem. They don’t own you or have any right to your creativity. And if someone contacts you to complain, they’re being an entitled jerk.
7) Remember number one. While some people may be disappointed that you’re going in a direction they don’t want to follow, other people will be delighted that you’re going somewhere else they like.
tl;dr: don’t worry, write what makes you happy, tag appropriately, and trust your audience to take care of themselves.
