I think you already did with Chaos legions. To consider them humans is heresy by your standards, am I right human?
From my understanding of God in 40K, they have power from 2 things: Emotions and Belief. Believing in a God enables them to work through (or corrupt) an individual. The Emotions one feels give sustenance to the Gods. This seems to apply to all of them from what i have observed. A few others (Chaos Gods for example) gain and grant power through sacrifices.
I don't know if I want him reborn again as a man (though this is probably for the best,) or if I want him released upon the warp as a full god.....which would make the Chaos gods piss their heresy stained britches. (Though, Slaaneesh probably hasn't worn pants in millennium.) Either way, it's on like Donkey Kong. Also, I see the Emperor as a living embodiment of all that humanity can/will become. He's just far ahead of his time evolutionary wise (with a bit of help, depending on how he actually originated,) and without him mankind would be prey to the various denziens of the warp and xeno races. So, basically, he's trying to get all of us on his level....gives us the opportunity to choose our lives instead of being dominated by him or the ruinous powers.
Adding other races e.g. Tau, they believe in what the Greater Good haha? Thanks some good answers in there.