I never understand this "advance the timeline"! argument. I think this is a comic book mindset and doesn't apply to 40K. GW has ignored the internet as much as possible except now finally it wants to listen to the "advance the timeline"! crowd, well I think it bite them in the end. As for the idea of releasing a new Mk 9 armour that looks more like iron man so that it is easier to protect the IP of, well thats clearly wrong. There may well be a mk9 but moving away from the current Space Marine Astetic is a very shake idea alone. Space Marines make GW a lot of money and messing with that would be suicide.
Most likely...
40K will get split into 2 new core games.
30K "The Horus Heresy" . This way they can spam marines and make loads of money. They can use up all of that shelf space that WFB doesn't need anymore. FW can focus on all kinds of odd stuff instead of making billions of space marines that are more profitable in the long run in plastic.
41K "Millennium of Skulls" New marines here. Segmentum Pacificus will become a new "imperium secundus (again)" with Guilliman back in action. The rest of the imperium has collapsed.
The best thing is that most peoples current marine collection doesn't really fit in anywhere, except on the shelf. Congratulations you are now a Game Workshop Figurine Collector! GW was right along.
http://www.warseer.com/forums/showthread.php?404105-2015-40k-releases-according-to-BoLS/page24