Thanks for the comments! You hit on a lot of why our app is structured the way it is. I agree too, we could've put those investments into Next.js rather than migrating to Rails. The difference was with Rails I could envision what the endpoint looked like (codebase, costs, caching, dev env, deployment, hosting options, etc). If we were to invest that time Next.js, some of those answers were (and still are) unclear. Agree we could still get there, it just wouldn't be as clear a path.
That's a fair argument.
And to be clear (because my original comment might read as negative), I do like hardcover a lot. It might not work sometimes, but I still use it to track all my reading, because the ui is charming, because it has a good, open api and because it's very clearly made by people who really like reading.
Wishing you all the success you can get!