A year and a few months ago, I picked up a Dell TB15 to use with my new XPS 15 9550. Since then, the TB15 was discontinued due to hardware issues. Last December, the WD15 as the only available replacement, even though its link was USB C, not Thunderbolt 3 like the TB15. However, Dell has since released the TB16, which officially replaces the TB15.
Since January, Dell has replacing existing TB15 units with TB16 for customers who open a support ticket requesting an exchange. Additionally, it appears that Dell is, as of late April, proactively sending out TB16 units to those who purchased a TB15 unit from Dell.com—this is how I ended up with a TB16. In addition to the TB16, Dell includes a letter explaining the exchange process and a shipping label for returning the old TB15.
As the official successor to the TB15, the TB16 is extremely similar to its predecessor. It contains the same assortment of IO ports, and is physically the same size. Externally, the only change is the addition of two thermal vents, one on each of the two sides without ports. Internally, there is a fan that spins up after being powered for a while when driving a monitor.
In the case of the XPS15 (and other Dell products), make sure in the UEFI settings that Thunderbolt Security is set to “No Security”. This appears to be the only mode that works with Linux at the moment. In the other modes, only the monitor ports work. The Ethernet adapter and audio ports appear as USB devices. Frankly, it looks eerily similar to the WD15.
The Ethernet adapter is a Realtek RTL8153, which your kernel may or may not have a driver compiled in. If not, you can find it under Drivers > Network Devices > USB. The Audio adapters is a Realtek device. Again, this is a USB device (device ID 4014. This device appears to work with the snd-usb-audio driver.
Of course, the advantage over the WD15 is being able to drive more than just two 1080p displays. It definitely can drive a 4K display at 60Hz. Additionally, hot-plugging and hot-unplugging works.
[end of transmission, stay tuned]