Hmm. Not sure I agree with that. I think you are giving Irsay entirely too much credit. While I do agree that he would back, even promote, a tank job, I do not think he is intelligent or savvy enough to formulate such a plan. If so, he wouldn't have fired Polian afterwards, unless, like you said, Polian wanted out of football (I've no idea if that's the case).
If you remember, the Colts were all systems go in the 2011 offseason. The defense was virtually unchanged from 2010. They still had Mathis, Freeney, Powers, Bethea, et al. The offense had upgraded on the line: 1st rounder Anthony Castanzo (who busted) and the rest of the guys were the same (Addai, Wayne, Garcon, Clark, Saturday, et al).
It also doesn't make any sense given the timeline. In May 2011, Peyton had his third neck surgery, another in a series of relatively conservative measures, with the idea being to play the full 2011 season. I mean, he signed a 5 year $90 million contract extension in July 2011. So it was all systems go on Manning at that point.
Unfortunately for Peyton, his neck did not respond, and he was forced to undergo another, much more serious surgery in September 2011. The Colts team building had been completed at this point. Polian's mistake was that he hadn't drafted/developed a capable backup for Peyton, who'd previously never missed a game. There was literally no adjustment to be made, as good quarterbacks are not available on the free agent market at that time (usually ever, but at least you can sometimes pick up a game manager). In late August, the Colts had signed Kerry Collins, who was washed up and planning on retiring, when it became clear Peyton wasn't going to play. Polian rolled the quarterback dice, by essentially have one guy on the roster, and got badly burned.
Also, stepping back from it, Irsay certainly couldn't have predicted they'd have been the worst team in the league, and thus the winner of the Luck sweepstakes. It's not like the guys in the locker room are going to 'tank for Luck'. These guys are playing for career and contract extensions; can't afford that kind of mentality in the NFL.