Basically a hot Tokarev 51k vs 36k, and .308 dia bullets vs .311. Kinda surprised hot 30cal handgun rounds aren't explored more, modern metalurgy that can handle rifle pressures, and bullet designs that can make use of stupid velocities, do it in a straight walled or tapered case and get 2-6 more rounds capacity vs 9mm in the same size flush fitting mag
I think a lot of it is that the pressures involved do increase uncorking pressure significantly. So very loud. Not that big a deal with ear protection and less so if suppressed. But firing a 9mm in a hallway without ear pro is going to leave your ears ringing. Fire something with 50 or 60k PSI peak pressure and a pistol length barrel in a hallway without ear protection and you're going be doing the Stirling Archer "meep. Meep. Meep" as you dig a pinky in your ear and wonder why it is hard to heard anything around you.
A juiced 32acp could be pretty nice. Straight wall, 19mm case and 35-40k PSI, and you could be kicking out .312" 90gr bullets at probably an easy 1200fps. Easily take a Glock 17 frame to 21-24 rounds of capacity. Or make an easy, slimmer double stack pocket handgun with a 12-14 round capacity. Those kinds of velocities, easy to make a well expanding JHP projectile that'll penetrate deep.