Does it federate with other services? I have not seen anything mentioning this on the website and I consider it to be crucial for me backing the idea of this service. I don't want or need yet another centralized *book.
They say that they don't want to decentralize the service (as in, everyone can run their own instance), and I can understand their stand on that. However, they say nothing about federation with other similar attempts that are popping up.
Instead of "Will I be able to run my own instance?", think: Will I be able to follow an Openbook account from my Mastodon account?
It's something I've come to expect. If your hot new app doesn't federate, I don't care about it.