Thanks for the quick response, I read the long thread you linked and am very disappointed to see all the problems people are having with TB3 for this laptop.  The fact that this laptop "might require a few more firmware updates to get stable" makes me think it's not really ready for sale. Too bad given all the nice reviews, but most people buy this machine to develop on which means they want 2 - 3 monitors plus other peripherals. Given the limited # of ports on this laptop, its TB3 port really needs to support the functions of the TB3 spec, clearly it does not yet.

@codemasterg  I agree.  I don't have any sense for how widespread these issues are.  Obviously on a forum you're more likely to hear from people having problems than people saying, "Just letting everyone know that my system is working perfectly fine," and the XPS 13 is a very popular system, which can make it tough to gauge the affected population.  But it does seem that the "Launch it now and fix the bugs with updates later" mentality has been taken a bit far, although in fairness I don't think that's necessarily limited to Dell.  Laptops from other vendors seem to have some teething pains too, even flagship laptops.  For example, a popular Lenovo laptop had launch issues such as changing certain BIOS settings completely bricked the system beyond repair, or the inability to adjust the brightness of the built-in display.  Definitely frustrating for affected customers who just want and expect their system to work.

@codemasterg  It's not at all unusual for the product pages of accessories to have incomplete system compatibility lists.  But this PDF indicates that the XPS 13 9300 is indeed compatible.  There is an error on that PDF in that the 7390 and 7390 2-in-1 should indicate that the WD19 130W is compatible with the XPS 13 models only require 45W.  I've reported that to a Dell Support rep here, who confirmed that it was an error and will be fixed at some point.

However, the XPS 13 9300 does seem to be having some issues with Thunderbolt overall.  Here is one pretty long thread about this, and there are others.  Another thread found that a recent BIOS update broke the ability to use most USB-C to DP or HDMI adapters even though they work on the older release.  So it seems the XPS 13 9300 in general might require a few more firmware updates to get stable.  So you might see some issues, but if you do, it won't be because the WD19TB isn't compatible.  It is.

Thanks @jphughan.  I'm really hoping folks will reply to this thread with success stories (e.g. I am using the 9300 with docking station XXX, monitors YYY, and everything works as expected).  Every review I read for best Linux laptop includes this machine.  Since I intend to develop on Linux, I'm hoping there is a configuration that someone is actually using that works and that they can recommend.

There is another thread about this: https://www.dell.com/community/XPS/XPS-13-9300-and-WD19TB-linux-problem/td-p/7644488

It's likely not a good idea to buy this dock yet for Ubuntu (developer edition).