I think that the next game is going to be about the construction of another Mass Relay.
It doesn't make sense that if they had a standby that they would use the Second Mass Effect to just tell about a Huge Reaper and a recruiting process if there was a Second Relay some way. They said at the end "we'll find another way" not we have alternatives.
Theirs a Mass Relay being built somewhere where we don't know and it's going to be finished and the forces of all the Reapers are will class head to head with Forces of the Galaxy, the Rachni the Salarians, the Krogan, the Asari, the Batarians, the Quarians the Geth.
It's going to be about maintaining the alliances we've made to finish the job.