I think it’s ridiculously fun to have a variety of barrels that could be used. Like axlerod said, they don’t get switched all that often once installed.
I was going to make a three barrel rifle for one of the kids, but they have no interest in it - many just don’t like that it’s not just one caliber.
My current fun new-to-me switch barrels are 22 creed, 6mm-06, and an upgraded 308 win.
For a new shooter, a 22-250 paired with 243 and 7 mag covers everything well.
If someone already had those two, adding a 300, 338 or 35 cal would be fun.
The BR cartridges are fun to mess with - I have a 6br and 30 br and won’t complain when a 22br and 20br fall out of the sky.
Dad hunted all over Alaska with a 17 Rem, so I’d like to get a series of barrels (and bolt) with that 223 case head. 17 Rem, 221 fireball, 204 Ruger, 222, 223, 6-223.