Lawyers argued that under tikanga, Ellis' mana continued after death and he had a right to be able to restore it.
McKinnel said it would take some time to see how the law developed but this was "an incredibly important and proper decision".
"(If) somebody, even if they are deceased, has suffered a miscarriage of justice, it's going to able to be dealt with," McKinnel said.
"There's not going to be a collective shrug of the shoulders and 'oh, well, there's not much we can do about it'."
Open Justice asked if that could also be applied to historic cases, even stretching back into New Zealand's colonial history.
"I don't know whether it will or not but where there have been clear and obvious miscarriages of justice, and there is evidence to support that, in principle it would be difficult to put time limits on it."
McKinnel said the case was extraordinary not just because of its particular circumstances but in general, because Ellis was now deceased.
"It is, yet again, another demonstration of how long and how difficult the fight can be for somebody once they are wrongfully convicted."
The court held two hearings to determine whether the appeal should continue
despite Ellis' September 2019 death - in November 2019 and June 2020.
The June 2020 hearing concerned the relevance of tikanga Māori.
The Supreme Court judges said they accepted that tikanga considerations would support the personal reputational issues relating to Ellis' appeal being taken into consideration.
"As the tikanga experts put it, 'death itself does not close the door'," they said.
One of Ellis' lawyers, Kingi Snelgar, said it was great to see tikanga recognised in New Zealand's highest court.
"It's an exciting time and hopefully, more tikanga becomes the fabric of our legal system in the future," he said.
Currently the Criminal Cases Review Commission, set up in 2020 to investigate miscarriages of justice, does not accept applications on behalf of dead people.
However, at a Community Law Centre hui in Hamilton in September, chief executive Parekawhia McLean said commissioners would be watching the outcome of the Ellis case.
For the commission to consider cases posthumously there would need to be legislative change, she said.
Community Law Centres o Aotearoa chief executive Sue Moroney said cases should be investigated posthumously.
"Our view is that they should be because of exactly these sorts of precedents."
She said clearing a person's name after death was often just as important for whānau.
While there had been posthumous pardons before now, whether the family of Ellis could apply for compensation was untested in law.
Justice Minister Kiri Allan told Newstalk ZB she had sought advice around compensation for Peter Ellis' family.
Allan said at present, Cabinet guidelines did not allow for posthumous compensation.
But she said she's looking at whether or not an amendment should be made to allow for compensation to be made to his family.
She said as a precaution, she's sought legal advice in a bid to understand what that might entail.
Outside court today, Ellis' lawyer Rob Harrison said the team were not considering compensation and that they would work through the 152-page Supreme Court decision first.