Renowned iOS hacker MuscleNerd just tweeted not to upgrade iOS 8.0 if you need to enjoy jailbreak features further more. Here is his tweet extracted from MuscleNerd’s twitter profile.
To 2014’s new jailbreakers: if you update to today’s iOS 8.0, you’ll lose your JB and won’t be able to go back to 7.x. Beware!— MuscleNerd (@MuscleNerd) September 17, 2014
You will not be able to downgrade iOS 8.0 once you upgrade your device. The only way to downgrade it if you have iPad 2 with 4.X or 5.X blobs as he said. Apple released the new iOS 8 with hundreds of new features few minutes ago and It’s available on compatible devices to direct upgrade via Apple upgrade server. Check what you need to know about iOS 8.0 here.