The grammatical reference of the first phrase "and also others who have been" is obscure. There is no clear referent for the "have been" - there is a missing verb. The reference is directly to John and his writing, and so the implied verb would be "and also others who have been shown this vision." The Lord is letting Nephi know that his experience with this vision of the future history of the world and gospel is not a unique thing, but something which is given to others. In addition to Nephi and John, others have also written, and their writings are sealed up to come forth at a later time. At this time, we cannot say whether these records have been revealed, or are to be revealed. There are certainly numerous manuscripts which have come forth in recent years which might fit into this category. There might yet be other sacred writings which are yet to come. From our modern perspective, the import of the verse is not that we are awaiting more confirmation form other sources, but that these visions of the conclusion of the purpose of the earth are not isolated incidences - and that they shall corroborate each other.