There will be a lot more than 56.
PS Plus Premium will have 340 games split between PSOne, PS2, PSP and PS3.
People can make their own guesses about how Sony will split that but even if it's something like a 10/10/10/70 split (with PS3 being the 70%), which would be 238 PS3 games, that means the PS3 selection on PS Now losing nearly 200 games. If it's something like a 20/20/20/40 split, that's 136 PS3 games and nearly 300 games gone.