[coldtea]

It might be -- I've only got one 4K I've tried.

But Thunderbolt is not "proprietary" is an open standard adopted by the industry at large, including PC makers.

Also the "expensive Apple hardware (outdated $1000 monitors only" is not really apt. It's not that running dual monitors necessitates using old Cinema Displays. It's just that Cinema Display's are old, and Apple hasn't made any new monitors for a few years. But no need to buy/use Apple monitors for that -- and it would be foolish to buy them when there are 4K ones around by Dell etc. Apple even keeps a page with supported and tested third party 4K monitors.