Mr Ellis (61) served seven years of a 10-year jail sentence for abusing seven children at the Christchurch Civic Childcare Centre in 1991.
He was released from prison in 2000, but has always maintained his innocence.
It is believed he has only months to live after being diagnosed with terminal bladder cancer. This week, the Supreme Court granted him leave to appeal his conviction.
Dunedin author Lynley Hood, who did extensive research on the case and wrote a book - A City Possessed: The Christchurch Civic Creche Case - said she was "tremendously pleased" Mr Ellis' case had come this far.
"It's been a long time coming, and I'll certainly be watching with a great interest."
Dr Hood was careful not to say too much about the upcoming case, for fear of jeopardising the outcome.
However, she said the team of University of Otago staff, which included vice-chancellor Harlene Hayne and former law school dean Mark Henaghan, who had done "a huge amount of work" on the appeal, was a major factor in allowing it to happen after all this time.
"The weight of evidence has shifted so much.
"He's really in a much stronger position now to appeal than he was previously."
Prof Henaghan said that the team's work was built on the research of Dr Hood, and Mr Ellis' lawyer, Judith Ablett-Kerr QC, who spent many years working on it.
"They started the ball rolling and we've come in at the end [2017]. We've built on the shoulders of those two giants.
"It's been a combined Otago effort. A lot of work has been done and it's all been done in the Otago region.
"It's a credit to the brains trust we have in Otago."
He said the basis of the appeal was the "unreliability" of evidence admitted to the court by an "expert" psychiatrist and the children themselves.
The children accused Mr Ellis of carrying out ritual abuse and torture, but critics later took issue with the techniques used by social workers to interview the children.
Prosecutors were also criticised for relying too heavily on the children's testimony.
"It was argued at the time, but there is much stronger scientific evidence now to show, that there was a risk of quite strong unreliability with regards to that evidence - particularly the contamination of the children."
He said a psychiatrist was allowed to give evidence that the children's behaviour was consistent with their having been sexually abused.
"We now realise that you can't really give that sort of evidence because children's behaviour can be consistent with all sorts of different things.
"That sort of evidence cannot be given in courts now.
"At the end of the day, the standard of proof in a criminal case is you need to be sure beyond reasonable doubt, and I think if they had this [scientific] evidence that we have now, they wouldn't have admitted a lot of that evidence to court, and that probably would have made a substantial difference to the outcome of the case."
He said the case had been appealed twice before, but he believed the scientific evidence was much stronger now.
"With hindsight, we can see it a lot clearer.
"I think we've got a pretty strong case."
