@Melonlity -- It is true that the marching baritone has been a mainstay in high school bands for years and appears to be as popular as ever. However, you will not find as many of those instruments in orchestras and such. It would seem the bass notes are covered by other instruments such as the tuba or euphonium.
But, keep in mind that instruments appear to wax and wane in popularity. The good old baritone could make a comeback on the symphony and brass band set at any time. All it takes is a few influential people to bring it back and the popularity of that baritone horn will be on the rise once again.