I'm thinking of converting my .300 BLK pistol to a 9mm pistol for just that reason. I'd keep the .300 BLK upper, though. I like multipurpose tools...I wanted an easily suppress-able PDW type gun for uhh, “home defense.”
So either a .300blk SBR/pistol with expensive ammo I didn’t already have, or some 9mm PCC type gun that shoots ammo I have from mags I have.
It was an economic decision at that point.