The PS4 should definitely be their main focus, otherwise Sony won't be able to regain the market leadership they had with the PS1 & 2. The Vita and the PS3 will have to settle for whatever resources are left after the PS4 has been served.
The PS2's lifecycle was long and could've been even longer, if there hadn't been a transition to HDTVs. 4K TVs aren't going to become commonplace anytime soon, so in that respect the PS3 could have an even longer lifecycle than its predecessors. Sony is also going to be able to sell the Super Slim more profitably than previous models, so it would be great if they could keep the PS3 business going alongside the PS4.