The <40" OAL carbine in 30-06 pictured up thread holds 4+1 rounds, I think; that would do for me, but I would prefer the barrel 2" shorter still. If they did one for straight walled 357 cartridges, it just might have a slightly shorter stroke, and a 357 six shooter worn on the hip would provide sufficient extra firepower. Or even a pair in a double shoulder rig.
Mostly though, I would best like a reincarnation of the IMI Timberwolf 16" barrel, although there do seem to be very mixed reviews on 'em from the few who have them.
I was waiting with extreme impatience for Taurus to put out a 357 carbine Thunderbolt, until they did finally release rifle length 45LCs, and I handled one myself. No thanks. The CAS/SASS crowd jumped on 'em pretty quick, but too many of them did so with later regrets. Doggone shame.
(I had given my local FFL a green light to order me a 357 if/when they came out, sight unseen. Good thing they never did. Lesson learned.)
Anybody wants one in 45LC, I wouldn't be surprised if a NIB unfired one is not still sitting in the rifle rack at Sportsman's Village in Cairo, Georgia, with a layer of dust on it.
Like Craig said, seems nobody wants to make one that isn't westernized for CAS, more about style than function.