Are you willing to consider a setup without TB3 or are you definitely intent on TB3? While I certainly understand if you are, I ask because two USB-C 4K displays and a TB3 hub (so you still have a single cable to the Mac, which I assume is what you prefer) may be less-expensive and open more options...including Dell's 32-inch and 27-inch 4K Ultrasharp displays. I just purchased several U2720Qs and these are stellar displays (from the cable management perspective, it's a shame macOS doesn't support MST )
I am actually trying to avoid investing in TB3 dock or USB C dock capable of handling 2 4K monitors @ 60 Hz. Even today, TB3 docks are not yet perfect. I spent hours researching popular products from Caldigit, OWC, Belkin, and others. That's why I am looking for 2 monitors daisy chained via TB3.
Plugable is expected to launch TBT3-UDZ TB3 dock soon. It uses Titan Ridge chipset. I will consider this dock when it becomes available.