Johto being called new pokemon because Johto is maybe being re-introduced?
Kids of this generation did not experiance Johto thus most of them don't know much about them or haven't experianced playing through the game.
Some pokemon are legitly impossible to get such as Celebi or Lugia/Ho-Oh, 3 beasts/dogs without having games for another system such as Colo/XD.
It would be logical for them to make for these reasons.
1.) Highly demanded
2.) Big oppurtunity, Big money
3.) Fun and lets you complete your pokedex, also was the best gen and game of all time, having 16 badges, an Elite Four, and with todays modern updates it would make a perfect game.