You can play around in the guestbook. I'm in it right now and you can see me editing things.
Cloudflare Durable Objects are pretty cheap and I'm using it like a very basic pub/sub with each deck having it's own DO. I did some calculations and it should be well within my spend limits.
Something super small that I've noticed in the guestbook: since there're a lot of people connected, I noticed that every time I received an update, I lost the focus of my text element, so it was a little bit difficult to write something.
It may be annoying if two users are working at the same time in the same project.
Again, very cool project! :)
Yup, I've made a note of this and will fix it once the Show HN traffic eases off a bit. Thanks for the feedback and the kind words!