A tad off the topic, but what about a smaller display?
In essence, retina is a marketing concept pitched at creating a very detailed viewing experience. But it is dependent on your viewing distance.
In other words, I could live with a smaller display that has a greater pixel density. And a smaller screen has an absolutely smaller number of those pixels, which is why a little old iPad knocks the socks off a big old cinema display without the need for the same bandwidth/power/processing horsepower.
I haven't done the math, but would a 21" screen 25% closer to my face, with a retina display, be within the range of a nMP and existing outputs?