Oddly enough, I think that if someone brought out a new style weapon w/ a revamped/ renamed 30 carbine cartridge as the latest and greatest PDW that sales would be brisk! The regular action w/ modern sight options and synthetic furniture would be OK, but I think an FN P90 in .30 cal would be much more useful than that 5.7mm round- if armor piercing is req., then just use sabots or some such- probably would be even faster than the 5.7 w/ more base area to push on. Otherwise, there's tons of development in good expanding projectiles. All the 30 carbine really needs is a good facelift-in either the weapon or the cartridge.

I think the ultimate success of the round would be assured of it were able to be hot-rodded a bit, but that's not a good idea unless it was changed just enough to not work in the old weapons.