We do not have the blessing to the house of Ishmael. Certainly there is a continuation of the tribal organizational principle, but the blessing is not recorded. From Nephi's standpoint, the blessing must not have had a significant impact on the spiritual future of his people, and therefore was not as important for him to record as those of his brothers. It might also be that as a male of a different family, Nephi's history is simply uninterested in Ishmael. That would not be unusual at all in ancient lineage records.