This is a new feature, so it can go only in 3.5. Updating the generated HTML sounds like a good idea, however we must consider if this might cause any problems related to backward compatibility. If you are going to do this, please use (valid) HTML5.
Why we can't add this in 2.7? Major projects and OS supporting 2.7 now and I am updating this because I am need of feature for 2.7. Can't we do it like release new version with new name(or something like). If one wants to download it, he/she can download using pip and make it default in python 3.5?
Yes, you could make patches for Python 3.5 and release a PyPI package that includes these changes and it's compatible with older versions. The same has been done for other modules as well (e.g. unittest2 includes features that are available on recent versions of Python but it's compatible with older versions too). The reason why we can't add this to 2.7 (or even 3.4) is because they only receive bug fixes (and older versions only receive security fixes). Since there won't be a 2.8, new features can only go on 3.5. You can find more information about this on the devguide.
