Mr Nobody wrote:I'd like the Tau to have a more competitive role and be more of a contender on the galactic scale. Right now, they feel just a little too small for the
40k universe. Hopefully, this can still happen in a new codex, if we ever get one.
That is the whole point of the Tau though. They are similar in power to dozens if not hundreds of other species' in the galaxy who just aren't powerful enough to serious threaten well, any major faction.
As for the old Necron background, it appeared superficially sinister yet the Deceiver had been wandering around for thousands of years if I recall correctly, do little of importance other than potentially helping Abaddon out. Really, the fact that they were faction who actually had their gods stomping round should've catapulted them into complete ascendency but instead they just didn't do much. Meh. I prefer the new background. Destroying their gods strikes me as much more interesting.
Personally, I'd change the Tyranids from having bio-titans and such amazing regenerative abilities and the like. Make them rely on numbers rather than paradoxically having vastly superior numbers, brilliant adaptibility to the point of rendering select weapons useless and titans capable of bring down Imperial Legios and yet still actually being defeated. In contrast, I'd remove the vast numbers of Daemons and instead make each one much more powerful but harder to summon. Not sure how it'd work with Khorne Daemons; for a Bloodthirster to really be a threat you'd expect it to have considerable magical powers.