No different than all other PCCs.
Beretta CX4 Storm was originally restricted, but only because of barrel length. Then they came out with an 18.5” barrel that was non-restricted.
CZ Scorpion Evo 3, same thing. Only restricted because of barrel length, and NR with a longer barrel.
Sig is the same story. Either they come out with their own variant, or you have a new barrel put on and the length measured by a qualified gumsmith, and your firearm will become NR.
I thought the MPX was an AR "variant". Damn, I'm gonna hafta get one now. I already own a few non-res pcc's.