So a short MPX type weapon in 10mm?
Also, SMGs, at least ones like the regular MP5 are kind of obsolete in a world of good AR SBRs, especially for the average American, where the same tax stamps and hassle is required regardless of caliber.
However, if you're seriously worried about overpenetearion, and can ignore gun laws, modern SMG's like the P90 and MP7 have a place. The totally unsourced, third hand accounts I've heard from friends closer to the action say things to the effect of, "with a P90 or MP7 you can magdump a motherfucker really fast, and the odds are decent you'll need to"