Out of curiosity, what would you use a stronger graphics card for on a Chromebook? I thought all the video codec acceleration was on the CPU. Do you use a lot of WebGL?
It's not particularly hard to get ubuntu working on most chromebooks.
Not to mention even random web games (like slither.io) do better with a decent gpu, especially if your driving a monitor with more than 1080P.
Re: video decode acceleration, ChromeOS on Broadwell should support GPU accelerated h264/VP8 decode and hardware assisted h265/VP9 decode. (I might be completely misinformed about this though.) I'm not really concerned about the GPU performance with regard to video decode.