Interesting thing to note is that b1 is still being signed - I tried that on an iPhone a couple of days ago. Since the restore process sets the date/time though and the b1 expiry has long passed it makes it irrelevant so Apple probably doesn't stop signing the betas until GM release because there is little point. Going to test this with a 7.0 beta too for curiosity.
So basically, now that b2 has expired the only possible beta firmware that can be restored is b3. Does anyone know off hand when that is due to expire?
No way, 7.1 b1 is still a go? Even though it's expired? Worth getting my old iPhone 4 on it? 7.0.4 is just slow.