They could stick a GTX 1060 in there, like Razer has in their Blade 15. But that, along with the 32gb ram option, would probably result in a slightly thicker laptop with poorer battery life.
But that makes me wonder: why didn't they make the 12" macbook a macbook air, make the new 13" and 15" macbooks, and then come out with the slightly thicker, more powerful pro 15"... and maybe 13"
Apple is not competing against bulky, gamer-style laptops. For a thin laptop, the new mbp is extremely powerful.
Even if the fully upgraded, 15 inches mbp is sold at an astonishing €4999. Well, it's company's expense, right? :)