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-...