Assuming this is actually true...
Why would they need to leave the Milky Way? Less than 1% of the galaxy had been explored by the time of ME3. It's not like they were running out of living space or resources.
Also, how are they leaving the Milky Way? The Reapers, to our knowledge, only ever operated in the Milky Way (since they're off hibernating in dark space when they aren't harvesting us), and they're the ones who made the relays, so I doubt they constructed relays outside the Milky Way. FTL in ME isn't nearly advanced enough to allow ships to leave the galaxy in any meaningful span of time unless they found a relay that sits on the very edge of one of the galactic arms.
Also, "Khet"? "Remnants"? Really? Not even going to try to be subtle with those names and how similar they are to "geth" and "Reapers"? I guess the Remnants also created the massive relays, and the central hub of all the massive relays is the Bastion, the seat of galactic government. And the player, as Captain Shepherd, must defeat the Khet and their leader Jaren, who is under the control of the Remnants and searching for the Plug-in on Eyelos.
On the one hand, these rumors sound really stupid and probably aren't true. On the other hand, the rumors and leaks for ME3 were really stupid and turned out to be entirely true.