And even if you can't upgrade the internal GPU, you have 2 thunderbolt ports. Just plug in a new card.

Intel hasn't approved an external graphics card that can connect via thunderbolt, and probably won't for the foreseeable future. It's one of the big issues I have with thunderbolt -- it's micromanaged to hell and back.

Are you saying there is no all-in-one external graphics card?

Sonnet makes an external PCIe Thunderbolt enclosure that you can pop a graphics card into, and there is that DIY guy: http://www.extremetech.com/extreme/162652-diy-external-thund...

Granted that is not pretty and there are OS support issues. But it is possible and I am hopeful it gets easier.

The last time the sonnet enclosure came up it was determined that the bandwidth of thunderbolt is simply not yet enough for a high end graphics card (especially if we're talking about upgrading years from now) and the enclosure itself did not provide enough power (only 100-150w). Not to mention there are no reports of this actually working with any graphics card, let alone a high end one worth upgrading to.

Just to demonstrate the bandwidth of PCIe3 x16: PCIe1.1 x16, PCIe2 x8 and PCIe3 x4 all provide around 4GBps. That's right, not 4 Gbps. So that's 32Gbps times 4 for a grand total of 128Gbps over PCIe3 x16. In comparison, Thunderbolt 2 at 20Gbps is very constricted.

I'm not sure the external GPU route will ever be useful for professionals, but I'm hopeful that it will become a more viable option for gamers who want a laptop that is light and thin, and the decently portable option to plug in a midrange graphics card that would work way harder than any integrated graphics could.

ok RAM I'm wrong about but the GPU extension is not the same thing as being able to buy the Video Card you want. So if you want to upgrade to the latest version of CUDA you can't.