[derefr]

There's no reason that Thunderbolt (especially optical Thunderbolt) can't be that standard. In fact, there's no reason that Thunderbolt controllers need to live in the CPU, rather than living on PCi-e HBA cards (like InfiniBand or RAID controllers do.)

It just hasn't happened yet because of a lack of enterprise demand. The pendulum hasn't swung back to all-externalizing blade servers quite yet.

[namibj]

Actually they currently just put a retimer chip on the backplane, attach the NVMe drives to the otherwise passive (as far as high-speed data goes) backplane, and use QSFP+ twinax cabling between the backplane and a sometimes passive "HBA" card that adapts from PCIe slot to this QSFP+ cage. Afaik they can run PCIe3 x4 per cable. If you look for open compute hardware, you'll find various modular blade-like designs.