I think Amex stands a good chance, they have a ready database of potentially dissatisfied IT Gold members that should be easy to poach for Jet. Plus Amex haved prior experience of working with airlines at a reasonable scale which should also interest Jet.

I cant really see any bank as a potential partner other than HSBC/Stan Chart/RBS/Amex that Jet would see as the 'right' profile for a premium card. I would be surprised if they partner with an ICICI or HDFC.