In ONG §3.9.6, Gerald Browne suggests that the future tense is a tense like the present, and the two preterite forms. This seems to be mistaken.
1) The paradigm is more "dirty" the other three
2) The future morpheme -(a)d seems to behave like aspectual suffixes like inchoative -(a)ń and causative -(a)r
3) The attestation of a future preterite, i.e. -(a)d + -s: P.QI I 11 i 7-8: papina … -kid-d-es-il; P.QI I 7 ii 15-16: eisanenappa ńodou ńokinka istaurocildō olleirimen-d-is-a-
1) In Bechhaus-Gerst 2011, she argues that the "Old Future" in Nobiin (formed with -d) has a mainly aspectual, not temporal function.
2) The development of "innovative" future tenses in modern Nubian languages, like Kunuz with prefix bi-, seems to point to the absence of a "proper" future tense in ON.