It was coming, we all heard the rumours that the Imperial Guard were being renamed and despite the cries of the masses it went ahead. I have no real opinion on the matter, I don't think it will translate to the table top - long term 'guard' players are unlikely to alter their semantics and I doubt new players will either ("Astra Militarum? Oh, you mean Imperial Guard"). My bigger question is 'What was the point?'
The trend of late has been to release a new codex and put loads of things in new boxes. It started a bit with the Eldar and Space Marines but their new boxes were only for the new models. However, with the release of Crimson Slaughter, pretty much the entire CSM range got shiny new boxes. It will be interesting to see if this is the case when AM hit the shelves next week. If they do, then the rename becomes seamless, if it doesn't then you are going to have an army that is branded in products with 2 names.
Redesigning boxes isn't overly expensive but it is still a cost and as the IG have a huge number of boxes to revamp this could be an expensive process. On the long term view though, currently GW (presumably) has 2 printing presses - for the old and new style of boxes - this isn't necessarily the best way to go about mass production so maybe they are moving towards changing all of the boxes over time.
Or maybe it's not about the money maybe it's about the theme and style of the fluff. When you consider that the Space Marines are actually called the Adeptus Astartes, and the Sisters of Battle have had their own bastardised-latin make over, the Mechanicum too, especially FWs new stuff are filled with the gothic sounding names. All of the positions in Imperial society and organisation, the ships, planets and cities are aggrandised, maybe the IG rebrand is just to make them fit in with the rest of the universe. On reflection the term Imperial Guard is quite out of place when compared with the technical/elaborate names that the rest of the Imperium's forces have so maybe it's about continuity?
What ever the reason, it's happened and we as a community will just have to get used to it. I think that the reactionary cries from some corners of the internet are a bit much...after all, a rose by any other name will smell as sweet - a Basilisk by another name will still bomb the crap out of your deployment zone...