There're the way to create 1080p HiDPi on iMac 27"

[Amethyst]

I know this question like an idiot.

But I think if we can run 1080p-like desktop size on 2560x1440
rather than 720p-like It will be great.

May be create custom resolution by SwitchResX?

Taste the retinaaaa iMac.

 

[drjsway]

27" iMac + 720p HiDPI mode + 32 inch distance = retina display. That's the only way right now.