12GB of RAM in a phone makes no sense unless the IS itself was rewritten to be terribly RAM-inefficient. There's no way you're going to run even a huge app long enough to gather up enough in-RAM data to need 12GB - or even 8GB. Even running 3 large apps at once, with all of them holding a large amount of data may get close to 8GB, but I doubt if more than a handful of people use their phones like that. It's more a sales tool than anything else.
And, as Mike said, a 25mp sensor is also a sales tool. They're making thinner phones, and you don't do that with telephoto lenses and large image sensors.
But we'll probably see 16GB RAM phone - and even 24GB RAM phones - in the future. It's like using a semi to go grocery shopping.