On a game's page where you can edit the theme, it'd be a cool idea if you could embed a youtube video or iframe in place of a banner image.

That way, you could make something like your game's trailer the first thing people see when they look at your game's page.

Thanks for the suggestion. I think it's unlikely that we'll let people do iframes, but we may allow mp4's in place of images at some point in the future. (With transcoding to static images in some scenarios). In the meantime, if you want a trailer on top you can put it in the description of the page. Use the 'Video' button on the text editor.