You have to sign lots of NDAs and other docs, give company details, describe the product you want to develop, just to get a look at the datasheets [1]. To put that in perspective, the datasheets for their latest and greatest processors are very readily available [2]. Thunderbolt is very much an intel only game. I really wish that the PCI-SIG had gotten an open standard for external PCIe out, it would have been rather useful.

[1] https://thunderbolttechnology.net/contact/thunderbolt-develo...

[2] http://www.intel.com/content/www/us/en/processors/xeon/xeon-...

Intel is refusing to sell the chips unless you swear undying loyalty to Intel.

You do, but part of that license is validating it works and it's not cheap. It's part of the reason why thunderbolt cables are so expensive compared to their alternatives.