That class action talk has been around for years and years, and yet here we still are. They provide a long beta period and a number of weeks even after the release with the previous version still being signed. That said, being able to downgrade at least to the last release of the previous major version would certainly be good.Happily on iOS 8.4.1 on my iPhone 6. My hang up with Apple is they stopped supporting Snow Leopard with iOS 9 & 10 yet 9 supported Windows XP!
All iOS final versions should still be signed in order to support corporate enterprises and consumer trial testing.
Imagine if you installed Sierra on your MacBook and couldn't downgrade to El Capitain. Same thing. Someday a class action will force apple to keep signing.