Would expanding Melee Weapon Training (Universal) to include Melee Weapon Training (Primitive) harm game balance in any way? In general, it looks like it'll just save most PCs 100 or 200 xp.
Conceptually, I have a hard time seeing anyone capable of using high-tech versions of simple melee weapons of not being able to use the simple weapons the designs are based upon. In this line of thinking, note that Thrown Weapon Training (Universal) already covers the Primitive group, and this change would simply parallel it.