Yeah McKay's been given a bad rap. He played that unimpressive Test at Perth and burst that bubble of hopefulness that had been surrounding him. So he could be getting himself in contention for that 4th quick bowler for the first Test, along with Siddle, Harris and Bollinger (although if Dougie's fit I imagine he's locked in as the #3).
And for the World Cup I think he should go ahead of Siddle as the 5th quick bowler. Johnson, Bollinger, Harris, Lee and Tait are ahead, but one of them will surely have an injury by then.
As a bit of critic of McKay. His problem is basically as a test bowler he doesn't do much with the ball, he is just straight up & down @ a standard 13-135 ks. He could pass as a ODI bowler sure, but should be way down the pecking order for tests.
In tests outside of the main 5 quicks of Bollinger, Hilfy, Midge, Harris, Siddle. I'd be picking/considering George, Cameron, Starc, Copeland, J Pattinson before i think about seeing McKay in the whites again.
For the WC next year. Lets not forget he wont be getting any pitch like the one he just took 5 for on (although a few green tops might pop up). Generally its going to be very good batting decks, thus i remainded unconvinced how effective he could be in general on such pitches. Theirfore once fit & based on peformaces in the Ryobi cup the 4 quicks that should be in the WC squad are Bollinger, Tait, Harris, Johnson as you said. He & Nannes are the immedaite back-ups to those 4 ATS. Of course Lee if his pace returns the more cricket he plays in the Ryobi cup, he could be fast-tracked right into the main squad.