I'm interested in a solution to this too. VMWare Fusion has a "Use full resolution for Retina display" option in the VM's Display setting section--it's unchecked by default, in which case Fusion scales the display up 2x so the guest isn't tiny and illegible. Macs aren't the only machines that have high-DPI displays though; PCs have them too, so it seems like Workstation needs the same option.
Also, View -> Autosize -> Stretch Guest is grayed out for some reason... if that would work, Workstation at least be usable on a high-DPI display. It looks like Stretch Guest is available in full screen mode; any reason to not have it in windowed mode too? Finally, even in full screen mode, Stretch Guest doesn't work properly... the mouse location is really messed up. E.g., if I move the mouse pointer near the lower-left of the guest desktop and hold down the mouse button and move it around, it shows a drag rectangle near the upper-right of the desktop--very far away from where the mouse is.