The XPS 13 convertible is returning next month with refreshed Intel 8th gen Y-series CPUs. Dell will be sticking with the same design, but they have suggested that the series has been successful enough that a full refresh will almost surely happen sometime down the road.
https://www.notebookcheck.net/The-XPS-13-2-in-1-is-coming-back-with-Intel-Amber-Lake-SoCs-for-1000-USD.320376.0.html
Latitude 7390 2-in-1 is the real deal, not XPS. A likely explanation for crippling the CPU is that Dell probably doesn't want the XPS 13 2-in-1 cannibalizing their best-selling clamshell model.
Jerry,
XPS 13 2-in-1 is significantly more portable. If you are getting a convertible, that matters huge.
David, the Latitude 73xx series are based on XPS 13 hence they share a nearly identical chassis and form factor. And there are numerous 2-in-1 alternatives that surpass either of these laptops in terms of portability.