Question have you considered giving the 40K system the ability to combine forms within reason. Like a skitarii and a necron Warrior perhaps at the cost of 1 or both of the old forms or maybe even insert image here Just an idea I thought was interesting
I would have exchanged the system for the God Emperor, you'd get intelligence that rivals gods of intelligence, powers the put most Sorcerers to shame and knowledge, especially how to create the various troops, for example the Astartes.