BR
That works well enough by having the animation outside the 4:3 zone, making it a bit less empty.
They used a widescreen mock up (I think) on a promo recently:
http://tvnewsroom.co.uk/wp-content/section-images/sky-sports-promo-transfer-window/TV-Newsroom189729.jpg
Video
http://tvnewsroom.co.uk/wp-content/section-images/sky-sports-promo-transfer-window/TV-Newsroom189729.jpg
Video
That works well enough by having the animation outside the 4:3 zone, making it a bit less empty.