PS4 News - UPDATE on Downgrading systems, someone has successfully done it - YouTube
It is apparently possible to revert your PS4 to its previous firmware version, without any backup - Wololo.net
ps4 exploit for 7.51 or downgrade? | Page 13 | GBAtemp.net - The Independent Video Game Community
Wololo on Twitter: "PS4 Syscon keys allegedly disclosed, could ultimately mean PS4 downgrade is possible https://t.co/beD9Qvy5eT https://t.co/XIsZeeI1pP" / Twitter
Il Primo Downgrade PS4 - Playstation - Gamelite.it