Do you have any idea how much space is in between galaxies? How did we get there? The Mass Relay network doesn't go there, and that's the fastest form of travel in the galaxy as of ME3. If the relays DO go there, that's a serious retcon, as there is absolutely ZERO evidence of that in the first 3 games. And in fact, if the relays do go to another galaxy, and the Reapers built the relays, there should be Reapers in the other galaxy.
It's basically a gigantic cop-out. Though ME3 was so screwed up a fresh start may very well be the only thing that can salvage the franchise.
Who knows? Maybe the existance of Reapers in the other galaxy will be the new game's "Big Surprise" that will be sure to earn 10/10 5-star ratings on the box printed before the game's release.