Even then, Windows machines aren't future proof. Case in point, last year I built a workstation for school and virtualization. Maxed it out with 4790K i7, 32 GB of RAM, SSD/HDD RAIDs, 4 GB graphics, etc. Total cost, with dual monitors, was around $2600. That's pretty spot on for a decent iMac - and that's not even including the 5K display, and it runs Windows (lol).
Oh, and you know what? Sure I can upgrade the machine I built, but if I want to change ports - PCI or new motherboard. New CPU? Change the motherboard. You get my point. The perfect does-it-all future proof computer doesn't exist. And if it did, it would be over $3000 and still be outdated in 6 months!