Any half decent lawyer can drive a bus through the "you only lose PSN if you stay at 3.15". The publicity that came out right at the start said that you'd eventually lose the ability to play the latest new release games. As soon as you restrict the principle reason for the PS3 to exist in the first place (play videogames) then you are in the shit and it has nothing to do with access to PSN. Losing the ability to watch BR movies Sony could possibly argue around, but not losing out on access to new games. Yep and making it not possible to play MAG on day 1 of 3.21 release is bad too. No way Sony can reasonably argue that 3.21 is optional with the only loss suffered being access to PSN.
Sony could easily find itself on the back foot on this if the court accepts the argument that as an advertised feature they can't remove Other OS support if it comes with the consequence of losing other essential features.
If Sony can find a way to prevent access to PSN but still allow online FW updates only that bypass 3.21 for the Other OS users (therefore you can still play all new disc based games (other than MAG) and watch BR movies) then the only valid and potentially legally sustainable argument is removed.
“The fundamental cause of the trouble is that in the modern world the stupid are cocksure while the intelligent are full of doubt.” - Bertrand Russell
"When the power of love overcomes the love of power, the world will know peace."
Jimi Hendrix