4k monitors are still so much more expensive and have noticeable costs on laptop performance at least. When I got a macbook air with USB-C, I was initially planning on getting two 4k monitors. However, that would mean spending ~$500 to get a 27" monitor, $120 for a thunderbolt adapter than can drive both displays at their proper refresh rate, and >$200 if I wanted an adapter that can also charge the laptop.

All told, that's the total price of the laptop just in periphery. I ended up going with a $30 usb-c adapter and some ~$100 dell 1080p screens, and I'm happy as a clam.