With stuff like the Vita consoles are going to come to an end soon. That much power is now in such a small device and consoles won't be needed as much in later years.
And you can just plug that stuff to a tv if you want to play on a bigger screen.
Not true at all. You need a big screen to play games properly. Portable console games are created delicately just so you can play and see the interface correctly on the small screen, whereas almost any game could be played on a big screen.
EDIT: Not that you can't carry around a big tablet however, but there's a threshold before a portable screen becomes too big to carry around.