The problem with Thunderbolt is that it’s only 20 gigabits. Even Thunderbolt 3 is only 40 gigabits. As long as you’re using an external connector, the connection just won’t be fast enough. I have a Thunderbolt eGPU, and it’s nice. But it requires a significant amount of compression for Thunderbolt to be sufficient. There’s never going to be an external interface which will be as fast as an internal one.In near future not only cpu will be soldered, also pcie expansion will be an luxury option and surpassed by Thunderbolt, we will see pc with only Thunderbolt 3 and usb-c/display port 1.2 connectors also for power/charge.
Maybe the PCIE video card would last a bit more will be the last pcie peripheral offered on the market eventually doomed to be ruled by usb-c/Thunderbolt 3 and mostly non-upgradeable Barebones.
Just like the car market, notwithstanding how eye poping is tuning cars, every year is more complicated and more and more exclusive, people now is not usual upgrading they car's, also the stereo which was the most popular upgrade is now doomed and every year more complicated or inconvenient or just impossible.
So when people think on upgrade an car is unlikely to think on a more powerful engine or stereo, most people think on sell and buy a new one.
The computer consumer market is walking the same road but much faster.
Though, it makes me wonder if Apple wants people to make Hackintoshes, especially considering that they made it easier to make them shortly after making the new Mac Pro.