Hi,
To be fair many GMs have to attempt to rp many of these things in a single session, albeit on a more temporary timescale. Hopefully, with either Tau, Eldar, or any other xenos, enough fluff will be included that even the most inexperienced 40k'er would be able to make a go of it. As has been pointed out already, many of the "human" concepts currently available are so far out of our 21c terran existence we may well fall short of accurately rping them also?
Be fun to have the option though..