User blog comment:Rusty650/About the Idea of "Mass Effect 4"/@comment-65.185.166.118-20130627013119

We know that activating mass relays was considered dangerous by the council, which led to the first contact war, and Liara mentioned in 3 that we aren't as widespread as the Protheans. So, not every mass relay was active during the events in our section of the galaxy. If the dormant relays prevented the crucible from transmitting it's signal to other parts of the galaxy, there may be unknown sentient aliens still fighting reapers. Another trilogy with a different council or empire might be interesting.