Most professional stadiums display the pitch speed, albeit usually on one of the auxiliary boards rather than the main video board.

Thanks to enhanced pitch tracking in the last few years, they can now display even more information. The Pittsburgh Pirates' first- and third-base ribbon boards show pitch speed, vertical and horizontal break, and IIRC even the name of the pitch (bucketed based on the speed and break characteristics). It's a really neat addition to have in real time.