Oh, and I missed the middle part of your post. Fair question! I do think it is quite sustainable. For that to make sense you might have to know me better, but my perspective is I have a good paying job, I have money and especially time to spare and I want to make things better. So I'm honestly happy to spend money AND time on this to be sustainable. I have a very capable root server to run this on and I have money already reserved to get another one. I'm getting by just fine and I'm more than happy to spend some hundreds of euros a month to make the world a little easier/better for people. I'm also happy to spend my time for this.

I did think a lot about monetizing it, but really I feel like that would skew the whole idea of the app. I want this to be for the community. We struggle enough with enshittification anywhere. I'm in a privileged position where I can build and maintain this. And it's available for self-hosting, so anybody can do so as well.

Now, if we were to hit an insane amount of users, the question might have to be tackled again, but that's far away and I think with the infrastructure I have and can get with my allocated "solidary" budget, It'd really have to get to insane amounts to actually be an issue.

So I'd like to think it is indeed sustainable. I'm doing this to be sustainable. I want to build something people appreciate and use. I'm happy to spend lots on it!