I know it's an old thread, but this is the first I've seen of a bullpup conversion for the Hi Point carbines, which are good PCC's for the money. I've been on a bullpup bandwagon for a couple weeks and do think a pistol caliber bullpup would be an extremely good choice for home defense given the shorter length helps in controlling the gun, making it easier to work in tight spaces, not as loud as a rifle cartridge, and cheap to shoot.
But, those limited to 10 rounds, I think the bullpup design is tough to recommend with how often you may have to reload. The Kel Tec or Cx4 would work fine for you guys, they're only a few inches longer than this. Free states, this Hi Point bullpup with a 20 round mag would rock.