I'm of the internal-cards over external-cables school of thought. I've been plugging circuit boards into backplanes since the S-100 bus era, and I'm very much committed to the idea of a discrete computer chassis containing all the major computing components as a distinct entity compared to the screen. I still have desktop machines because of this.

Thunderbolt 3 ports are closer to PCIe 3.0 x4, not x8. Regardless it won't cause a huge performance hit depending on your workload (about 5-10% slower in gaming benchmarks). But YMMV with applications that require more bandwidth.

I mean, the Trashcan Mac Pro had Thunderbolt expandability too. But that doesn't seem to have been as much as people were hoping for then.

which then need 2-500 chassis, or overpriced RAID arrays to do anything useful with...