That's really a shame...the average person just has no idea how critical the cleaning & lubing regimen is on a muzzleloader compared to a modern rifle shooting modern ammo.
Boring it out to a .56 probably wouldn't get rid of the pitting anyway...it would simply remove the .54cal lands making it a .56 bore...going to a .58cal would work, but as others have said, it would probably cost as much or more as a new barrel...if you could even find a place that could do it properly.
Make a wall hanger out of it, or a floor lamp, etc?