I'll just quote Green _Is_Best from the previous page to answer both of these misguided statements, because he hit the nail on the head and put it better than anyone else.
To advance the story past 999.M41 by telling the tale of a star system or two that was ravaged by Chaos and giving the Tau a bit more territory is not advancing the story at all. If you want to advance the story, something grand must happen, and that is going to upset a massive part of GWs IP.
Imagine if Abaddon was killed in the 13th Crusade. His not being a playable character in 5th Edition would be the tip of the iceberg - in the background his death would send shockwaves throughout the galaxy. The Black Legion would be weakened, if it didn't totally implode and split into separate warbands like the World Eaters, the other Traitor Legions would jump on this weakness to assert themselves as the dominant Legion - meaning Chaos would, as a whole, become enbroiled in much more infighting, if not out-and-out war within the Eye, and would cease attacking Imperial systems while they sorted things out amongst themselves..
Meanwhile, now that the Chaos heat is off, the Imperium can focus its attention on taking the fight to its other enemies. A war with the despicable Tau seems likely - they seem like a very tempting target, being a small (defeatable) upstart civilisation that can be realistically crushed into the dirt before they get a chance to gain a meaningful foothold in Mankind's galaxy. One good offensive to deliver a crippling blow and BAM! No more Tau codexes on the shelves.
Now that Mankind has a much more secure position in the galaxy, what with two of its enemies reduced to nothing, the setting no longer feels like Humanity's last stand, and the terrifying, apocalyptic doom and gloom backdrop that characterises 40K is lost. Humanity is now on the offense, the aliens and traitors are on the back foot and its an Age Of Hope.
Would you really want all this to happen in the story, and want to wait patiently for months and years for GW to update codices and novels, and then want to listen to every man and his dog moan about how GW got this wrong and that wrong, and how there is this discrepancy and that discrepancy, just so you can have another 1000 years in which to picture your battles?
Would it not be less selfish for you to simply imagine your battles happening in any of the previous 40,000 years of galactic history?