Since there is an already working draft for the picture and source elements, why not use these instead of divs?
Using the shiv for unsupported browsers that document.createElement('picture') and document.createElement('source') can make this future proof, even though the specification might change in the near future.
[...] even though the specification might change in the near future.
that's the issue.
if the specifications change, we would have many websites out there using the tag in a wrong way
if you ask me, this is a bad idea at the moment.
most likely it won't change, they boast it in their group site http://responsiveimages.org/
+1 to Scott’s comment, on behalf of the RICG. It would be good to have the original markup working in a branch, but it’s too early to change it over altogether.
I personally favor more conservative markup. +1 to @scottjehl’s suggestion of waiting a bit.
A branch would be great.
Also, if we end up polyfilling the srcset attribute for that approach, we might want to keep it as a separate JS extension/file so it can be optionally included for those who want that syntactic sugar, as the more complete polyfills I've seen for that can be somewhat heavy, and a polyfill'd approach to srcset won't bring any benefits that I can think of over existing media attr. capabilities.
The TAG has requested that the RICG put together a web component version of Picturefill, intended to follow the spec to the letter using custom tags but with x- prefixed element names to prevent what @Zauberfisch describes. That might better solve the original issue.
That work is (just now) underway at https://github.com/ResponsiveImagesCG/picture-web-component
We could also make the tag names configurable instead of having separate branches for each implementation. I like the idea of x- to bring it more in line with the spec while not causing future issues.
Thanks for your ideas here. We're closing this out as Picturefill moves to support the new standard markup landing in browsers. So, I guess that's kind of a fix! :) Thread here: #125