I dunno who told you the Wii U was 720p-only. Mine ran at 1080p all day, every day - albeit some games used upscaling to reduce the graphical workload.

JPEG XL provides comparable image quality to ordinary JPEG compression at around 80% of the file size. It also supports lossless encoding at smaller sizes than PNG, and can handle layers, transparency and CMYK, so in principle it could conveniently replace almost every existing raster image format.