The simulator is good for testing features and themes, but when it comes to designing themes, things can get very tyring, especially for players with a tiny screen. I dare you to stay for an hour improving a theme's design on a tiny window. Your eyes will stark blinking and you'll eventually become blind.
So, maybe a resizing feature (1x, 2x and 3x, for example) would help out. I didn't find anything about this, but I think it would be a nice addition.
It's just an idea, anyway, feel free to keep or scrap it.