The fight did around 325,000 buys which isn't really bad for a Super-Bantamweight fight. AJ comes close to doubling those numbers, so I'd imagine a joint main-even card with Joshua fighting a voluntary or even a weakfish mandatory could still probably do around 700,000 buys, which on it's own will generate around £13m. Like I said earlier, it would depend on Quigg winning a fight or two beforehand, but for all we know, the picture could look very different in 12 months time. What if Frampton loses to Russell Jr or loses to Santa Cruz in a rematch? What if Quigg moves up and beats Selby? The fight suddenly becomes attractive again. Let's not forget that Frampton was hardly a decisive winner against Quigg. Quigg gave him some hairy moments, but ultimately waited too long to put any form of pressure on. I actually think it would be a great event over in Belfast, especially with AJ on the card.
I think you are seriously over-estimating Frampton's money earning potential. He only took home $500,000 from the Santa Cruz fight. He took home £1.5m plus a percentage of the PPV from the Quigg fight. A rematch with Santa Cruz isn't going to generate much more money than the first fight. Neither is a fight with Rigo or Russell jr (fights he has a slim chance of winning).
As for Warrington, I'm not even suggesting he deserves the shot, and I'm certainly not suggesting he is deserving of having the fight in his own backyard. However, I easily reckon he could get 20,000 - 25,000+ into Elland Road for the fight. It's a money maker and an easy nights work for Frampton.