I’m new to jailbreaking aTV, but not new to the scene with other products. From what I can tell, we need to get our firmware signed by AppleTV as being current before we can update to our jailbroken version. What I’m wondering is if you are primarily using your aTV as a media server player, and for things like Hulu, than who cares what Apple gives or doesn’t give us? Why can’t we setup our own “signing” server, and redirect our aTV to look there for signed licenses? Then at that point, if aTV does an update again and no longer signs the last version, we don’t care because our server does sign them, and we need to merely redirect to firecore rather than gs.apple.com or whatever the link was? If something like that were to be done, what would be the downfall? We can no longer get paid movies from aTV? Like that’s what you are all jailbreaking these for? 
That assumes that we know how to calculate the required signatures. I do not think that is the case.
That’s what TinyUmbrella essentially does for you - it stashes the reply from Apple whilst they are still signing the version of your firmware. Then it allows you to redirect your hosts entry to Cydia instead of Apple to “sign” your firmware request. The problem is, if you wait too long Cydia can’t help you if Apple stops signing the firmware and you haven’t already got it stashed…
That was my problem. I hadn’t decided to jailbreak my ATV until the 9th, and by then, after hours of trying, I found apple was no longer signing the firmware. I had never jailbroken ATV before, so didn’t know about the limitation.