I like creating large, detailed worlds, but I find that at the current scale of 1 pixel per block, my template images end up being several gigabytes. It would be very useful if there was a scale setting in the config to change the number of blocks represented by a pixel, so that images could be made much smaller with only a minimal loss of quality

I have considered this, and almost started implementing it once, but I was unsure of how to handle the scaling/biome lookup on the sort of diagonals and other non-axis-aligned borders of the template biome colors.

So this getting added is a definite possibility. However I've been super busy with my client-side mods for the past year or so, so unfortunately I have currently no idea when I would have the time or would get a sudden burst of motivation to work on this particular feature...

A feature being requested or talked about is however an effective way of directing my attention towards it, so... we'll have to see. If this sticks in my brain such that I think about it and come up with a nice-ish implementation for it while doing some IRL stuff, then I might even end up adding it fairly soon.