Hello! not sure if you would welcome input or not... but im a helpful sort, so forgive me
i shall share my observations that i have made over much playing and lurking on E and beyond, you may use them as you will.
i would like you to succeed in forging a 40k RP, however, the.... issue that i have seen with your post (and my supposed reason for the apparent lack of interest) is a lack of a certain.... precision of vision.
a few points to consider:
-40k is a deep, rich and complex setting, people who would be most interested by a 40k RP, also tend to prefer deep, rich, and complex roleplay. a weak plot will have more trouble drawing players than a precise one, your plot amounts to 'chaos is invading! .......... okay have fun!'. we 40k-people are often more picky than that
-40k is not a setting for pussyfooting around, its appalling, brutal, violent, and riddled with insanity and darkness. 'Combative' role plays rely on recurring clashes between players, when it comes to 40k, this tends to end badly in one of three ways: A) somewhere between 'half' and 'all' of your players are dead by the end of the first 'phase' of the RP, this is the 'realistic' way, but reducing your players will naturally kill off your RP. B) if they are allows to remake new characters... over time those characters will become simpler and more 1 dimensional, as despair and lack of ideas begins to set in, which will kill your RP as sure as a anchor tied to your ankles in the middle of the pacific. C) if no-killing is in effect, the lack of death and true-violence creates a kind of... dissonance between what the player expects of 40k in general, and what they are getting from your RP, which will manifest as dissatisfaction, and also run your game into the ground.
-the most successful games plant all the players on one side, and provide a NPC faction to slaughter. You can see examples of semi-successful games Here
-the Grim Dark Introduction to 40k is both awsome and iconic, and using some version of it would certainly help to drag people in, kicking and screaming if necessary.
For more than a hundred centuries the Emperor has sat immobile on the Golden Throne of Earth.
He is the master of mankind by the will of the gods and ruler of a million worlds by the might of his inexhaustible armies.
He is a rotting carcass writhing invisibly with power from the Dark Age of Technology.
He is the Carrion Lord of the Imperium for whom a thousand souls are sacrificed every day, that he may never truly die.
To live in such times is to be one amongst untold billions. It is to live in the cruelest and most bloody regime imaginable.
This is a tale of those times.
It is a universe you can live in today – if you dare – for this is a dark and terrible era where you will find little comfort or hope.
If you want to take part in the adventure then prepare yourself now.
Forget the power of technology, science and common humanity.
Forget the promise of progress and understanding, for so much has been lost, never to be relearned.
There is no peace amongst the stars, only an eternity of carnage and slaughter, and the laughter of thirsting gods.
But the universe is a big place and, whatever happens, you will not be missed...
For in the grim darkness of the future, there is only war!
need i say more?
-Final point, the Tau make the best enemy, since no one but traitors and heretics like them, and they squish most satisfactorily when you put a powerfist in their smug faces. *nods seriously*
anyway, thats my 2c, i hope any of it is helpful!