There are many reasons High Guard needs revision, but to dig up the decayed corpse of the dead horse just to have at it with a flail once more:
there needs to be a unified technical architecture that is used to produce the 3ed Robots book, 3rd edition Vehicles, 3ed High Guard, a fixed Field Catalogue, and Central Supply Catalogue. It should scale, it should include lots of different tech paradigms, and then can be adapted by authors or referees to their setting.
Any technology meant for the Third Imperium as the default setting should be clearly labelled as such.
Speaking of which the current version has flipped bay weapons on their head, the screen rules are needlessly complicated and the combat system is still... lacking something.