It's the out-clause, combined with the uncertainty of what the wider Blues coaching team may look like next year that is blurring what should have been a straightforward business.
Blues assistants Mick Byrne and Graham Henry are standing down after this campaign and an announcement on their replacements is a few weeks away.
Nonu has never denied that his heart - and his immediate family - are in Wellington. And confirmation that the Hurricanes coaching team next year will be led by Chris Boyd and John Plumtree will have lit a flame within him.
Boyd is a Dave Rennie-type character - calm, measured, astute and capable - and Plumtree managed to get the best out of Nonu when he was coach of Wellington.
With both Alapati Leiua and Tim Bateman leaving, the Hurricanes are in desperate need of a bruising second-five. Nonu would give them what could be one of the most potent backlines in world rugby - TJ Perenara, Beauden Barrett, Nonu, Conrad Smith, Cory Jane, Savea and Matt Proctor.
There's also a sentimental backdrop. Next year may be the last Nonu plays in New Zealand. After the World Cup he may go overseas and the idea of playing his last campaign in Wellington will hold appeal.
Attempts this week to ask Nonu about his plans were stonewalled.
Kirwan will be wary of Nonu's situation overshadowing Saturday's must-win clash with the Crusaders and he'll be a little miffed, too, that it has even reached this point.
After reaching into the fire late last year to save Nonu's career, Kirwan would be justified in thinking he could expect a little loyalty in return.
Until that point Nonu was unwanted by all five New Zealand teams and had been granted permission to take a sabbatical, this time in France.
But Kirwan - who felt betrayed in 2012 when Nonu gave a verbal assurance he'd be staying, only to change his mind two weeks later and sign with the Highlanders - went down the forgive-and-forget route and offered Nonu a two-year deal with the expectation that he'd honour it in full.