content: Customization in general really. Cortana is nice, but I'd like some varied theme options and be able to have an extension operate as natively as a bookmark menu. I think maybe Microsoft might always be hesitant in the extension department, mainly because a good portion of their userbase (my dad) will install whatever extension a site asks him to so he can get to the content, this is a big security risk as far as I know, please correct me if I'm wrong.