Yes, we know that better performance and multithreading would be nice, but doing this is not a simple matter.

You can scale the window (e.g. to double size) using the method detailed in the wiki.
https://powdertoy.co.uk/Wiki.html?id=full-screen_how-to

Arbitrary resolutions will not be made, since all saves must have the same fixed resolution. This fixed resolution will not be increased any time soon (as it would make the game even slower than it already is).