Upscaling 720p to 1080p vs upscaling 768p to 1080p
With a good-quality upscaling filter (bicubic, for example), there's no particular importance to the 3:2 ratio. Starting from a higher-resolution source will produce a better-looking final image.

It's true that if you're programming the upscaler from scratch, making one for a fixed ratio like 3:2 is much simpler than making one that handles arbitrary ratios. But image-processing software, monitors, etc probably have arbitrary-ratio upscaling built in anyway.