For how long do users of Microsoft Office 2013 get free updates and new features that come out?

Thank you for invitation ............

Well I thinks once a Ms Office has a new edition I think it will remain its features until another edition will launch.. the only thing that I know in adding a feature is synchronization on mobile, pc , with ondrive or cloud storage.

You mean what is the life cycle of office365? Check out following links

http://www.allyncs.com/docs/lifecyclesupport.html

and definitely Microsoft pages