The previous gen Thunderbolt display effectively brought all the useful ports[1] back to the MacBooks with one cable, and made even the Air viable for a professional. It certainly was a big factor for me back in 2011.
Unfortunately with the current 5k display, the three included ports aren't even USB 3.1 gen 2. Like many other pros, I prefer to have dedicated keyboard/mouse, speakers, and Ethernet, and would have been happy to run a second cable if it brought those things back.
Right now it's looking like our best 'pro 5k' option is duct taping a hub[2] to the back of someone else's display. And it's not clear which hubs support the 15" MBP 87W charging requirement.
Feels like such a missed opportunity.
[1] https://www.amazon.com/Apple-MC914LL-27-inch-Thunderbolt-Dis...
[2] https://eshop.macsales.com/preorder/owc-thunderbolt-3-dock/