Sad, but true. The shoutbox at the top of the page has a bunch of controls on the "content" things like length of the shout, number of shouts in a row a person can post, how often they can shout (cooldown period between shouts), you can ban, block, or limit individuals, edit and remove individual shouts, and two levels of history. Once we move the shoutbox to one of the main body columns, all the controls are about how it "looks" like how many pixels tall & wide, text formatting controls, is it collapsible, does it have a title bar, but you loose a bunch of the content controls. So, no, if we leave the shoutbox in the right column, there isn't a way to limit the length like we can at the top.
I can put a notice at the top asking people to keep it short, but that's about it. Does it look tacky?
Should I make the box taller? I like to try to make the page as a whole look OK for people who have lower resolution screen sizes. And as more devices go to wide screens height becomes more of the issue.