Not sure exactly what you’re suggesting here.
Has your team considered utilizing the empty space left over when you hide the chat window?
When you close the chat (right sidebar), we expand the video player to take up the empty space. So yes, we have considered and implemented a method of recovering the lost space
attic.cyanstudios.ca/image1.jpg & attic.cyanstudios.ca/image2.jpg
This seems to imply you actually want a method to adjust the width of chat, which seems like a completely different feature request. Feedback of this type should be sent to feedback@twitch.tv so that Product can evaluate it and ask further questions if necessary.