Why would Joseph Smith take a chance on saying John the apostle didn’t die?

The Book of Mormon claims that John the apostle didn’t die, but instead remained on earth. 3 Nephi 28:6-7 reads:

And he said unto them: Behold, I know your thoughts, and ye have desired the thing which John, my beloved, who was with me in my ministry, before that I was lifted up by the Jews, desired of me.
Therefore, more blessed are ye, for ye shall never taste of death; but ye shall live to behold all the doings of the Father unto the children of men, even until all things shall be fulfilled according to the will of the Father, when I shall come in my glory with the powers of heaven.

The traditional understanding is that John died around 100 AD, however some early Christian documents claim, like the Book of Mormon, that John never died. One example is the Discourse on the Abbaton (not translated into English until the 20th century) which says:

And as for thee, O My Beloved John, thou shalt not die until the thrones have been prepared on the Day of Resurrection, because the thrones of glory shall come down from heaven, and ye shall sit upon them, and I will sit in your midst. All the saints shall see the honour which I will pay unto thee, O My beloved John. I will command Abbaton, the Angel of Death, to come unto thee on that day, and he shall not be in any form that will terrify thee, but he shall come unto thee in the form of a gentle man, with a face like unto that of Michael, and he shall take away thy soul and bring it unto Me. Thy body shall not be in the tomb for ever, neither shall the earth rest upon it forever. All the saints shall marvel at thee because thou shalt not be judged until thou judgest them. Thou shalt be dead for three and a half hours, lying upon thy throne, and all creation shall see thee. I will make thy soul to return to thy body, and thou shalt rise up and array thyself in apparel of glory, like unto that of one who hath stood up in the marriage chamber.
– E. A. Wallis Budge, ed., Coptic Martyrdoms in the Dialect of Upper Egypt (London: Oxford University Press, 1914), 492–493.

Where would Joseph Smith have gotten this idea from, and why do early Christian documents provide support?

See:

Evidence Central – Book of Mormon Evidence: John’s Translation

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