you’re looking for a 4K display that can be paired with your 12″ MacBook via a single USB-C cable, then your options are fairly limited. It seems that LG is one of the few display makers that has such a monitor available for sale.
LG’s 27UD88-W is a 27″ USB-C-enabled display. Its USB-C port allows MacBook owners to connect a single cable to drive the display, charge the machine, and facilitate data transfer.
This is actually quite cool. Too bad the colour’s not even close to that seen on the new Retina iMacs, but still. It does however need a hack to run at 60 Hz (see my next post).