As mentioned in the article, macOS works best using true 2x integer scaling. Using 2x scaling, a 4k monitor will result in an equivalent workspace to a 1080p display—unusable for productivity and development. A superior option is iMac/LG 5k display results which nets an equivalent workspace of 1440p.
The only options for greater-than-4k displays on the market currently are the 27" LG 5K ($1200, 2014) and the Dell 8k ($3500, 2017). I'm convinced this is due to the manufacturers focusing their attention on the high-margin gaming market which has no need for resolutions higher than 4k.
I'm holding onto my 30" 2560x1600 Apple Cinema Display until I can get something that offers me the equivalent amount of screen real estate at 2x retina scaling.