Well apart from Plasma, and possibly Flamer there aren’t that many restriction
Like in the lore we have:
Melee:
- 2H Hammer
- 2H Axe
- Spud Jacker (Wrench)
- Power Maul and Brute Shield (Suppression\Assault)
- Axe
- Flail
But could introduce:
- 2H Power (Industrial) Hammer
- 2H Power (Industrial) Pick
- Slab Sword
Ranged:
- Multilaser
- Heavy Bolter
- Autocannon
But could introduce:
- Lascannon
- Goliath Hand Cannon
but many could be invented, like the only thing not allowed are the Charonite stuff