as far as I know, Gregory of Nyssa was an universalist beyond the slightest doubt, an Orthodox clergyman whom I wrote an E-mail and rejects universalism affirmed this.
and even if he were not, which authority is he?- he lived in the 4th century as far as I know.http://www.biblicaluniversalist.com/QuotesFromGregoryOfNyssa.html
The ancients used words like "eternal", even "endless" in a quite loose sense, which I will show a further example from the NT:
οτι λυπη μοι εστιν μεγαλη και αδιαλειπτος
οδυνη τη καρδια μουThat I have great heaviness and continual sorrow in my heart.adialeiptos
is one of the words of which is said that the ancient Jews used to denote everlasting punishment, even this word is used here in a limited sense.
it's foolish in my opinion to focus on the words translated "eternal" or whatever, when the rest of an author's writing clearly shows he believed in universalism (or annihilation in some cases).