A "1/2x Display" option would be great! Command-0?
This might be a useless mess (or require grayscale AA) on a typical low-DPI Windows setup. But on a Mac (or other 2x "retina" display), this would give us 1:1 Playdate pixels instead of the usual doubling.
Depending on your screen and chosen resolution, this may actually be closer to the Playdate's physical size. On my 4k 24-inch screen, for instance, it would make a better preview than the current size.
Plus, when doing work on a small laptop, it coule be a welcome space-saver on your screen. (For that purpose, you'd either shrink the accelerometer/crank wheels too, or simply widen the yellow window to normal width to fit those controls when visible--but allow the yellow window to be smaller when they're hidden.)
Lastly. this would prevent wasted pixels when grabbing a screenshot or recording using the system or 3rd-party tools. (Those things are already nicely 1:1 when exported via the Simulator's toolbar.)