AFAIK, GPU is soldered to the Mainboard on MacBook Pros, as is the CPU. I don't see any feasible (easy) way to upgrade GPU? IMHO, not worth the hassle to rework the motherboard, even if you COULD figure out how to do it with a compatible GPU.
BTW, I've done the same BT LE/Airport card upgrade on my MBP. It is still working great for me, with latest High Sierra. (My main motivation for handoff was for the Hot Spot function...) I just go into recovery after MacOS updates and turn off SIP and then make sure CAT is active and running. Then I turn SIP off again with the "--without kext" modifier. Anyway, if replacing the GPU was as simple as this upgrade, I'd have done it a long time ago...
Apple likes to solder everything to the Mainboard now, so you can't upgrade anything anymore....which is one of the reasons why I haven't had the incentive to spend $$$$ on a new MBP. I've tried out models since 2013 at the Apple Store, and frankly don't see any real performance improvements that justify an almost $4K spend just to match my basic specs from my 2011 MBP. (Quad-core i7, 16GB RAM, 1TB SSD). IMHO, Apple has abandoned the enthusiast/evangelist segment. I still prefer MacOS and the Apple ecosystem between my devices, but my next notebook will likely NOT be an Apple. I completely disagree with the HW design choices, lack of upgradability, and product lifecycle management choices/strategy they've made. It is exactly the opposite of what made me be an evangelist in the first place. If you need a new computer today, I cannot in good conscience recommend Apple anymore over the competition...they just don't have anything these days in the Mac lineup to justify the obscene $$$ difference over the competition. I guess the fundamental issue is their Mac Product lineup just doesn't "delight" me anymore... ;-) The most disappointing thing is that it is now obvious they simply don't care they've alienated all of us enthusiasts who helped them sell computers and the ecosystem in the first place. Such is life... I guess when you can't innovate effectively anymore, you just build planned obsolescence into the products so folks just throw them away and buy new. Problem is, often those folks don't end up buying YOUR "new", but rather your competitor's "new", which often invariably provides better value.
Tip to Computer makers: You are missing competitive advantage in not producing products which allow for easy upgrades for parts that wear out or improve faster than you can release new product: Hard Drive, RAM, W-Fi, Battery, GPU, CPU. I firmly believe that the company who goes back to designing products with these components in "modular", replaceable form will see higher sales over the competition. (Especially RAM, HD, and battery). I also believe this is possible, and still adhere to the "thinner is better" model...