I agree with Kevin Butler as spokesman for PS4. There could even be a whole thing with him getting his job back and the running gag of "Unimpressed Yoshida".
As far as an actual mascot, I'd go with the robots. Sack Boy would be an awesome mascot for PS Vita. The thing with mascots is that they should have mass appeal and not just appeal to one demographic. Drake and Kratos appeal more to the "hardcore gamer" demographic than everyone while Jak and Daxter could appeal to everyone and have games made that appealed to casuals, hardcore gamers, adults, children, new gamers, and old school ones. Kratos could only have violent, edgy, bleak games. You couldn't even fit him into a children's cartoon if Sony wanted to try it.
Now Nathan Drake could be fit into a setting to appeal to pre-teens via an animated series to promote the PS4. Sony characters like Crash, Tomba, Sack Boy, and the PS4 ninjas all have that Sonic, Mario, Donkey Kong, Kirby-range of appeal though.