The Avengers are lost in time, eh? It looks like we are approaching the endgame of Aaron's run on Avengers.
Back in Avengers (Vol 8) 20, Daredevil, at that time empowered by Hofund, delivered a prophecy to She-Hulk:
The Celestials are still watching you. They powered you up for a reason. For war. But not this war. Or the wars yet to come. Through the hell race and the drawing of the heralds. The sea trials and the fury of Khonshu. The red rise of America's mightiest heroes. Through it all your gamma will burn brighter. And you will know when it's time to explode. When you come to the war beyond whens. The war you've already lost.
Jason Aaron normally uses prophecies or future visions to foreshadow the plans for his books.
Most of these have already come to pass:
they powered you up for a reason - The Final Host (Avengers 1-6)
but not this war - War of the Realms (War of the Realms 1-6 + Avengers 18-20)
through the hell race - Challenge of the Ghost Riders (Avengers 21-25)
the drawing of the heralds - Starbrand Reborn (Avengers 27-30)
the fury of Khonshu - The Age of Khonshu (Avengers 33-37)
the sea trials - Enter the Phoenix (Avengers 40-44)
the red rise of America's mightiest heroes - Heroes Reborn (Heroes Reborn 1-7 + Heroes Return 1)
you will know when it's time to explode - World War She-Hulk (Avengers 46-50)
So what's left?
'the war beyond whens' and 'the war you've already lost'
These are probably the same thing - the Avengers going back in time to meet the previous iterations of the Avengers.
All of this is building up to a big Avengers vs Mephisto event, probably in Summer 2023, which is when Aaron will end his Avengers run.