It's called 22TCM, I believe. On paper, it's superior to 5.7, but uses pathetically small expanding bullets as opposed to fragmenting long-ogive projectiles. I think 22TCM with the same actual Vmax bullet characteristics as 5.7, but loaded to 223 pressures (would obviously need to be made of the same actual brass) would be incredibly effective, though perhaps not from a very short and light weapon.
The primary reason 5.7x28 can't get much hotter is because it's fired exclusively in blowback and semi-delayed blowback guns (P/S90 and five-seven, respectively). Any higher in lighter platforms, and you get case separation as the case extracts under pressure.
The real shortcoming to 5.7 (that comes with a matching benefit) is the primer pocket is HUGE compared to the case head, so it can swell and loosen under high pressures much more readily than a small primered 9mm, for example. Makes reloading a low-reuse proposition (Teflon coating doesn't help, either). The benefit is the case is narrower (I think) than even a 32acp, making it extremely unique in terms of capacity. The five-seven holds 20 rounds, which isn't that impressive, but this is mostly due to the size the gun happens to be. Though the round may be X% smaller, that doesn't translate into X% higher capacity since we have to round down to the nearest whole round. A mag much larger has significantly more capacity (the 50rnd P/S90 mag), and I imagine a mag a bit smaller would be very high capacity for its size (for example, I'll bet about 10 rounds would fit in my currently 7-round R51 mags if they were .05" longer --that's a nearly 50% increase!)
TCB