If you take the three consoles: Xbox One, Wii U and PS4, only the latter severely limits the user. The rest give the possibility of backwards compatibility. Now, when you get a chance to run games from the playstation 2, which was released almost a thousand for retro-gamers will open a wide range of names.
Sony has planned to make a surprise to fans of the consoles, giving a second life to a 16-year old Playstation 2. No, not that consoles will go back on sale. Just now games from the PlayStation 2 will wind up on the Playstation 4. Information about this is not so much, except official statement that the team is working on an official emulator Sony 2 Sony 4.