**Concept**
Alright. Lets go outside the box here:
Something happened...... During the Reaper War, The galaxy was unified and the final battle to defeat the Reapers was being waged in the Sol System, Circa 2186. Armed with the largest and most unified coalition the galaxy has ever witnessed and the mysterious "crucible" and led by Commander Shepard, it seemed like Victory was possible against the Mighty Reaper Horde of Darkspace.
But during the final stages and events of the battle, something...... Went wrong. The crucible failed to fire and/or was rendered useless, the Reaper Armada was destroying the coalition and the military's of the galaxy were facing incredible loss and devastation.
Always the clever tactician, Admiral Stephen Hackett of the Earth Systems Alliance, put into effect the ultimate back up plan.
For years The Earth system Alliance and with the help of Salarian STG and the infamous "BlackWatch" Turian Spec Ops unit, have secretly developed a Time Travel device, capable of sending ONE operative back or forward 100s or years. The technology is untested, but there is no choice. Knowing that the cycle was lost and Shepard was incapacitated or KIA. Hackett greenlights "Operation Rouge Spear". One N7 operative is sent through the device in hopes of preparing the galaxy and finding out what happened in 2186 and the crucible device......
But.... Something has gone astray. The N7 Operative awakes to a unidentified star system that matches NONE of the systems of his/her Cycle.
This is.... Mass Effect Shift.
The main narrative and storyline is you're the "Hero" and you must find a way back to the correct place and time. But along the way you find that things are not all what they seem..... And there may be even a more sinister and viscous force "out there" than the Reapers ever were.......
So yeah, maybe something like that.