That was totally awesome and terrifying... a few questions though; what happened to the still-living Eldar gods, and what about that Necron time travel guy? Surely the introduction of 'traveling into the past, even if only for a short, temporary while' would have some effect?
A Mind that can talk to itself from the future, a la Sufficiently Advanced (a free roleplaying game set completely independent of either setting, but... interesting... see: http://www.1km1kt.net/rpg/sufficiently-advanced or http://www.1km1kt.net/rpg/SA_web.pdf ) might be interesting, don't you think? Also, stable wormholes from one side of the galaxy to the other would probably be possible at some point in the tech timeline you mentioned... which would definitely be a big deal, yaknow? Those do exist in the canon 40k galaxy. But consider mining that PDF for tech ideas, maybe..
Also... you are either a dull enough soul that the Tau thing works, or you are a bright enough soul that the Ork / Tyranid fields can work. One or the other... they are mutually exclusive, I believe...