When all browsers will be able to support HTML5 100%?

It is expected that in year2020 all browsers will be fully supported HTML5

if you conisdering IE6,7,8 & other older browser then it will never but if all browsers means latest browsers then I guess not soon in near future considering it ongoing process Html5 is just new version of html with new features incorporated in html development. There is a race & gap between browser development & html development if particular browsers come up with support of some new features of html5 then html5 will come up with more new features in form of new version.