Agreed, I would never have bought a rMBP if it didn't come with a decent dGPU. I used to build high end gaming rigs, now my Mac more than suffices.
It doesn't need to be a gaming laptop to be able to game well, the 750M is a great piece of silicon, I'm just hoping that the Broadwell refresh includes something like a GTX 850M or 860M - both of which should give atleast a 50% boost to FPS and both of which have a lower TDP than the 750M, everyone wins.
Thunderbolt PCI-e bridges really interest me too, would love to be able to hook up some cheap 970 GTX to this and get some serious gaming horse power. So far I've only seen some less than ideal home-brew solutions.
Well that's fine by me, A I have a three year warranty (for free) and B, I plan to sell as each subsequent update is launched.