Although we are definitely meant to spread the gospel to all people, I'm not sure that is what is meant by "the gospel to all nations... and then the end." It appears that this is referring to the witness that Paul and others bore to the heads of nations when they were brought on trial before various rulers before the temple’s destruction. Notice in the following how that statement is sandwiched in between two statements about going on trial before rulers:

“you will stand before governors and kings for my sake, to bear witness before them. And the gospel must first be proclaimed to all nations. And when they bring you to trial and deliver you over, do not be anxious beforehand what you are to say”

Sounds similar to what Paul said about how the he was thankful when brought on trial because through it the gospel was being preached to rulers (And he was thankful that even those accusing him had to preach the gospel themselves in order to explain the charges against him to the heads of regions and nations). It seems to me like this witness before the representatives of nations and peoples is in fulfillment of what is meant by “the gospel being preached to all nations” in Jesus’ apocalypse.

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C. Gorsuch
Glencullen Baptist
Portland, Oregon