The LG ultrawide monitor with Thunderbolt that I have from a couple years ago (34UC97) mostly does this — It has a two-port USB hub which I use for my mouse and keyboard, which it routes either through the Thunderbolt interface to my MacBook or a separate USB cable to my PC, depending on whether Thunderbolt or one of the DisplayPort/HDMI display inputs is selected.
(I'd guess their newer models work similarly but I haven't confirmed.)