Interesting article, but of course one can almost feel your bias. Although I have been constantly struggling to fulfill file size restrictions for banners for almost 10 years now, I strongly disagree with you. I don't think it would be a wise decision to raise the mark to 400kB. On a "normal" website there is not just one but several of these banners and the amount of data transferred only for ads would easily sum up to several MB (even considering everyone would use the same frameworks and libraries). For mobile devices this would do nothing but promote the use of ad blockers.
My suggestion would be a tiny raise to maybe 100-120kB at most. This would promote a more subtle and more user friendly approach in ads which I believe is - in the long term - the much better solution.