We’ve found that sharing works better when the message is customized rather than automatically generated – allowing you to use social media features such as @mentions, add context, and overall provide a better experience for both you and your followers: https://goo.gl/Ezpt7Y
But @TeamYouTube it is already possible to custimize the message on the upload-page. Everything you could do here on twitter was already possible. Including hashtages, mentions and so on. What are you talking about?