Just doing some quick back of napkin maths, even assuming Apple's 128x128 app icons, and 48 bit colors (32 is more typical), we're still talking about a sub-100 kb max for a favicon.

So if Chrome set it even at 20 Mb that would still be orders of magnitude more than any favicon should be for at least the next five or so years (even assuming 256x256 became common for app icons).