There's not enough time left to meaningfully fill another 500,000 pixels; there's still a ton of white space on the current canvas. If the place time was shortened, it would have to be down to something like 5 seconds to be impactful. Changing the "rules" to that extent this late in the game feels silly. There's plenty of empty space as it stands.
500? maybe not, but i think it would be okay to resize it by 250 pixels instead. Not too large to be left out blank, and not too small for larger artworks to be made
Why did we resize at all? This completely prevented all competitions about space that makes the canvas so much fun. A lack of resources sparks creativity!
If you do choose to expand though, maybe make it so you have a pool of maybe 8-12 pixels that can only be used for fresh canvas and then 4-6 for overwriting?
As shortening for non-touched pixels seems there could be an exploit to get more normal pixels?