Thanks for the details. It sounds scary, but I hope you guys live long enough to see the other side of the tunnel!
Some thoughts from someone who is preparing to deploy on the fly.io platform soon (I will be hosting a poker app) -
I’ve seen reliability issues frequently during development. And every time I come across something, I wonder if I should post in the forums, or just assume that this is bound to happen and build around it. I’ve mostly chosen the latter, because I can imagine that a lot of these issues are probably already in your todo list, and will eventually get addressed.
The downside of that is, I have been spending non-trivial amount of time building a mini nomad within the backend (to orchestrate fly machines, and deal with unexpected failures). This makes me uncomfortable because I am not very experienced with this domain. However, one feedback is - if you can provide better APIs to listen to machine events for an app, or atleast query them with a 10s level of granularity, it will be a great help. I can again understand that this may be a very niche use case, but it will drastically improve the ability to react to fly’s infra failures for an application, should the application choose to do that.
Good luck to you all. Hopefully I won’t regret launching on top of fly 
PS. there’s no other offering that is offering what you are, and I have really enjoyed working with fly. So I echo the sentiments in this thread - if only your sandwiches held firm like grilled sandwiches.