An interesting tidbit appeared in the Belkin Customer Service twitterstream:
@kevinallgaier Just a li'l bit more, Kevin. We're glad to inform you that the Thunderbolt 3 Express Dock HD will be available sometime June.
— BelkinCares (@BelkinCares) April 27, 2017
The Belkin website still lists “coming soon”. Whether it’s an interesting device will very much depend on the price, about which Belkin has remained silent so far.