He's obviously an exceptional player, but yeah I just can't quite figure out how he'll slot into their current midfield trying to play something that resembles Ajax-Barca-City ball. He's literally been the shithouse player in the most successful team designed to stop that brand of football. Unless he changes his game you then need another new one or two midfielders to play alongside him (assuming Erikson can sort of do a Luka Modric impression) and you're either going to leave a tonne of space between the front three and midfield or the back four and midfield. City and Arsenal will get through that from three press with ease and Liverpool and Spurs will just bypass him over the top.
But like you say maybe they're going to drop him in and see what happens.