HK's won't be made because HK holds their brand pretty close to the chest. GSG pretty much got a cease and desist letter.
They do make 9mm AR15's. You just have to look for them. Several different companies make them.
CZ Scorpion would take a complete retooling as they cannot import anymore scorpion kits. Cost intensive for what would amount to a niche toy.
CZW is just too ugly to reproduce.
Thompson Contender? or Tommy gun? Auto Ordinance makes Tommy guns in rifle and pistol configurations already. Heavy and impractical.
On the HK note though, you can still have an HKMP5 semiauto... I just had one built on an original HK parts kit.
Now, it's waiting on SBR paperwork so I can put a stock on it.