Ran into your article, Dating the Book of Revelation, on the net. The Hegesippus evidence is actually addressed in John A. T. Robinson's "Redating the New Testament." Both Domitian and Nerva were in Rome during 69 and 70 AD, while Vespasian and Titus were campaigning in Palestine. They had delegated imperial authority in Vespasian's absence. Hegesippus could simply be mistaken about the dates, confusing events that happen in 69 or 70 with similar events in 95 or 96.
The only mention of Hegesippus in John A.T. Robinson’s book, “Redating the New Testament,” as it relates to my point is the following:
“Apart from quoting Irenaeus, he [Eusebius] refers to ‘the record of our ancient men’ (i.e. in all probability the Memoirs of Hegesippus) for the tradition that ‘the apostle John also took up his abode once more at Ephesus after his exile’ under Domitian’s successor Nerva.” (Robinson, p. 223)
Robinson makes no effort to refute this statement accredited to Hegesippus. In fact, he supports the premise by citing Victorinus’ statement that “John was ‘condemned to the mines in Patmos by Domitian Caesar’.” (Robinson, p. 223) Robinson goes on to cast doubt about the viability of these statements by citing Origen and Tertullian. The reader is not informed that Origen and Tertullian both lived decades after Hegesippus. It is unfortunate that Robinson would take the admittedly vague statements of Origen and Tertullian as more creditable over the unrepudiated statements of Hegesippus and Victorinus.
Concerning the theory that Domitian and Nerva were in Rome at an earlier date, Robinson addresses this issue as well. He credits G. Edmundson as the originator of that theory. Edmundson points out that Domitian served as a de facto emperor for the first half of A.D. 70 in the absence of Vespasian and Titus. (Robinson, p. 249) It also turns out that Nerva served in a consulship to the emperor Vespasian a year later. (Robinson, p. 250) Edmundson argues that Domitian could have banished John to Patmos at that time and Nerva could have released him a year later. That theory would place the writing of Revelation after A.D. 71 as John wrote the book of Revelation after he was off the island of Patmos (Revelation 1:9). However, this theory does not account for the statements of Irenaeus and Eusebius. Irenaeus said John wrote the book of Revelation “toward the end of Domitian’s reign” who died while serving as emperor in 96 A.D. (Against Heresies, V, xxx, iii, ANF, I, 559-560.) Eusebius records that John was banished to Patmos during Domitian’s 15th year of reign (A.D. 96, EH, III, xx,103). He also records that John returned from Patmos after the death of Domitian (A.D. 96, EH, III, xxiii, 104). This theory is only plausible in the absence of already known evidence.