It didn’t take long for Verizon and Apple to get their act together, and it looks like indeed Verizon using VoLTE (Voice over LTE) instead of falling back to CDMA will happen before the end of the year. The public beta of iOS 12.1.1 is out, and has enabled this.
I’ve personally confirmed this works using my iPhone XS with AT&T on the eSIM and Verizon on the physical SIM. As shown in the photo, you can see that Verizon is indeed not the active data line, which you can tell because it’s on the second/bottom row of the two carriers. Also the network indicator is LTE. The only time the network indicator is active for the non-data line is when in a call.
I would anticipate iOS 12.1.1 coming out early to mid-December.