With proper SIMD optimizations, the analysis to determine "nothing has changed" is so ridiculously fast that it's hard to compete even with direct XDamage output (or comparable things on other systems), whose data is not really in the format that an encoder wants.
Not saying there's no gains here, but people have proposed this idea before, and then given up on it after actually sitting down to implement it. It's also mostly an encoder optimization, and thus doesn't have much influence on the standard.
What's more interesting is adding special tools to the bitstream to represent things like text, which do not compress well with typical block transforms. This is certainly something we've spent some time thinking about, but there's no code committed for it yet.
Not saying there's no gains here, but people have proposed this idea before, and then given up on it after actually sitting down to implement it. It's also mostly an encoder optimization, and thus doesn't have much influence on the standard.
What's more interesting is adding special tools to the bitstream to represent things like text, which do not compress well with typical block transforms. This is certainly something we've spent some time thinking about, but there's no code committed for it yet.