Well, I personally see several advantages to a "fast" twist .30 carbine single shot. As mentioned, sub-sonic heavy bullet loads, coupled with a can, could make a VERY interesting camp/backyard gun.
Then there's fellas like "someone" I know (wink, wink), who're sitting on a substantial pile of the old GI .30 carbine ammo, even more handloads, and empty brass sitting there. I don't have it in mind to cobble up one of my .30 carbines, and the Blackhawk is earsplittingly loud.
I had occasion to meet a 'little grey-haired old lady' who'd come into Morris Sporting Goods (when Dennis still had the store down on Central Av. in Great Falls) who'd come in once a year for a box of WW 110 gr. soft point ammunition. Each year, she'd also bring in a photograph of the previous year's deer and speed goats that she busted with the rounds. Her rifle was an original, unmodified, War II issue Inland .30 Carbine, and she was absolutely lethal with it.
Gut-shot bad guys, if you listen to a lot of returning GI's, were barely fazed by the little carbine round, my Dad, a machine gunner in Korea, had two M2's in his hole the first night in country, next day, after a human wave came at 'em, and he ended up going to the shoulder guns, took the M2's down the hill and got two Garands.
For me, personally, the cost and trouble connected to the .32-20, .327, and other 'little' rounds just don't have enough going for them to make me pick them over the .30 carbine.
Fact is, that I've had my eye out for a decent Hornet to have rebored/chambered for the round.