[acdha]

> First you have to shiv IE to accept it as a DOM node

I find this an increasingly weak argument as it's applying to <10% of the market and falling fairly rapidly ahead of the 2014 Windows XP end of life and is true of everything else in the HTML5 spec.

> Then after the DOM is loaded, you have to re-write the DOM to replace the <picture> tags with <img>.

This is a reasonable complaint - I'm not sure I'd consider it a big deal since the work of manipulating the DOM is a lot faster than doing anything like downloading an image or rendering it but for anyone trying to do a wall of images it'd be worth benchmarking at the very least.