This article proposes that the gathering is martyrdom:

http://www.preteristcentral.com/What%20is%20the%20Gathering%20of%20Matt.%2024.29-31.html

I'm not sure if I agree or not but it is very compelling. It starts like this:

What is the "Gathering" of Matt. 24:29-31?

 

Matt. 24:29-31 describes the coming of Christ in the events culminating in the destruction of Jerusalem, AD 70. Verse 31 says "And he shall send his angels with a great sound of a trumpet, and they shall gather together his elect from the four winds, from one end of heaven to the other." What is this "gathering"? There are several views, but the one that we have settled upon at this time is that this is Christ's gathering the saints unto rest by martyrdom...

This article proposes that the gathering is martyrdom:

http://www.preteristcentral.com/What%20is%20the%20Gathering%20of%20Matt.%2024.29-31.html

I'm not sure if I agree or not but it is very compelling. It starts like this:

What is the "Gathering" of Matt. 24:29-31?

Matt. 24:29-31 describes the coming of Christ in the events culminating in the destruction of Jerusalem, AD 70. Verse 31 says "And he shall send his angels with a great sound of a trumpet, and they shall gather together his elect from the four winds, from one end of heaven to the other." What is this "gathering"? There are several views, but the one that we have settled upon at this time is that this is Christ's gathering the saints unto rest by martyrdom...