A new edition of Warhammer 40K came out over the weekend. We should probably re-tag most of the old questions as 5th edition to distinguish them from newer 6th edition questions.
I'd like to add that edition changes in games like 40K are non-trivial. Many questions would be greatly superseded by a new edition. For example this question is valid in 5th edition, but not 6th.
While we don't currently have many 40K questions, questions that specifically apply to the older editions need to be marked as such to avoid confusion.
The RPG SE uses edition specific tagging, because of the great differences you find in between things like 2nd, 3rd and 4th edition D&D. This is a similar situation. Most miniature game edition changes follow similar patterns of large scale changes.