Good call by GSP. Dana said he's willing to open his cheque book to make this fight happen, so if I was GSP I would see how serious he is. I'm sure he won't get $50 mil, but that's a good place to start his negotiation and maybe they settle in the $20-30 mil range.
I personally think this fight is going to happen, and everything that is going on now is just posturing by GSP. There's too much money and too much legacy at stake to not make this fight happen. And as Dana says, when the fans want to see something, the UFC will make it happen.