Thanks saulinpa but I'm only really interested in one with ethernet built in. The user has wifi issues in her office which we can't do much about and I'm reluctant to use a USB-Ethernet adapter as she's several hundred miles away and I don't want any hassles with that. The Ultrafine 5K is overkill, over-expensive and likely to over-heat a MBA. I wish Apple would hurry up with their rumoured new display, although that could be too expensive and too many pixels as well. It's mad that there are so few decent options for this.
Ethernet is old school as far as Apple is concerned so don't expect any new monitor from them with a network port. Next issue is that there are almost no TB monitors out there. There are USB-C monitors showing up that have extra USB ports but none with Ethernet that I know of. I believe one of the issues is that when USB-C is used for a monitor (alt mode) the basic implementations use the default USB 2.0 for downstream devices. It takes extra electronics to pull a USB 3 signal from the other links. Even more electronics for an Ethernet port.
What's wrong with a USB-Ethernet adapter? Otherwise your only viable option is a dock mounted to the back of a standard monitor which would have more hassles.