I think this would be a great deal... the Yanks would receive a failing pitcher who might start more games on the DL than on the mound, and could very well be a 4.50 ERA guy when on the mound. In return, they only have to give up a young, healthy good arm, who admittedly had a bad second half, but who has a lot of potential and a much better "upside" than Johnson has.
Any trade that weakens one of the monsters atop the AL East is a good trade IMHO...
Of course... I do have my Blue Jays coloured glasses on here