I replaced my bricked early 2011 MBP with a Lenovo laptop with a 4K screen at the end of 2014 (with pretty top end specs for ~$1200 CAD), so they've been doing it for a while.

On the downside, I got a consumer grade Lenovo, which meant free spyware and a less sturdy chassis than my MBP. Of course it was less than half the price of new similarly equipped Macbook Pro at the time.

Writing the response from my 3200x1800 13.3" screen. High enough for my tastes.

The 3K screens are seriously drool-worthy. I don't have a really pressing need to upgrade, but that 3K screen has gotten me wistfully playing with their laptop builder a couple times. It's literally quadruple the real-estate of my current screen (1600x900).