1: Remove the ads entirely. They make it impossible to browse.
2: Remove the automated copyright system and replace it with a team of lawyers that tell industry execs to fuck right the hell off on 99.9% of the videos they want muted. Unless there's a link in the description allowing them to download the audio, or the user uploading it is profiting off of it, then I honestly believe fan-made music videos, lyrics videos and the like fall under fair use. Not only that but it would keep people's home movies from getting fucked over because there was five notes of Enter Sandman playing in the background.
3: Invert the colors. Black background --> White text is easier on the eyes than white background --> Black text, and it will focus more on the video anyways.
4: When you're in full screen and you click on a new video, the page for that video is added to your browser's history. I can't count how many times I've surfed past an awesome video, or one I wanted to comment on, when in fullscreen mode only to find it nearly impossible to get back to it.
5: VEVO gets to DIAF.
6: The old channel style will come back. The new one still blows.
7: There will be no limits on subs in either direction.
8: Sending videos is only possible if the two users in question are friended. This should curb all the annoying spam videos that get tossed around.
9: There will be no facebook integration.
10: The support forum will be moderated.
11: Going fullscreen retains the same video quality the non-fullscreen video was playing in.
12: Favorites and inbox will have a link at the top of the page that, when clicked, takes you directly to those pages. No drop down menus required.
13: By default ALL videos on a given page will load, not just the first fifty. This may be re-enabled in your options if your computer sucks too much to handle it.
14: Subscriptions will update properly.
In short I'd pretty much just revert it back about four years.