Thunderbolt is not particularly “a drive interface”, it is a Jack-of-all-Trades (Master of None?) that is mostly used by Apple and on laptops (power, external display, screen-attached keyboard and mouse, and possibly wired Ethernet, all in one cable, yeah!). None of these hardware scenarios is relevant to TrueNAS, and compatibility testing would be complicated and expensive.
A request to support PCIe tunelling was officially rejected a mere four days after being opened. Seeing how long the average Feature Request can linger on (holding all the votes that have been cast on it) such a swift reaction certainly means something.