ABC needed a major star signed before the upfronts. I think that Katy would have to be on any list of major pop stars that ABC would put together -- I am pretty sure they were not redirected. Since The Voice has two of the biggest ex-Idols, the idea of an Idol finalist judges panel was precluded. [Kelly and JHud committed to The Voice before ABC got Idol.]
Adam would be a great judge but he is not a big enough star to impress advertisers. They needed someone big -- and Katy is as big as they get. The other contenders in her league are Lady Gaga, Bruno Mars, etc. None of the ex-Idols, including Kelly Clarkson, is in this league. Plus, Katy helps them sign the 3 major sponsors they are targeting. [Pepsi is looking like they might be on board. Coke already has The Voice.]
We know Adam really wanted the Idol judging slot in 2013 but that was before the QAL Tours and before he was signed to WBR.
The show was in LA and the schedule worked really well for him.
I can think of a few reasons Adam might not agree to be an Idol judge:
1. They don't offer him a great deal - enough money, terms he likes, etc. [Unlikely.]
2. Adam and his management decide that something else makes more sense for him and they pass. [Unlikely.]
3. Adam does not want to spend so much time in NYC vs. LA.
4. Adam and his management decide that a more limited role in ABC Idol is better for what he wants to achieve. He already is strongly connected with Idol and if he becomes a judge, that connection will be forged forever.
5. Adam is not available in Nov-December 2017 because of QAL so can only take some other role like live performance mentor.
I am not expecting to see Adam as an AI Judge for the 2017-2018 season but would be pleasantly surprised.
I am expecting to see Adam involved with the show in some way.
IF I WAS RUNNING IDOL -- I would pass on Ryan Seacrest and I would hire Adam as host -- pay him huge amounts of money and give him a monstrous, massive clothing allowance. He is charming, funny, quick-witted and would be great with the contestants. And it would be different to have a host who also performed. And I would have him perform every week.
#Dreaming!