But, Mr Peters would have to make it back into Parliament first after New Zealand First lost all its seats at last year's election.
Mr Peters was reappointed leader at his party's annual meeting in Hamilton on Saturday.
Yesterday, he said it was his "plan" to stand at the next election but said there were two more annual meetings before that.
It would not be hard to come back from outside Parliament, Mr Peters said.
"When I first got into Parliament I wasn't in Parliament, and I believe we can do it again."
During the last election campaign Mr Key ruled out working with Mr Peters if National won.
Asked today if he would extend that ban he was not sure.
"We'll cross that bridge if we ever come to it," he told TV One's Breakfast programme.
"I think we're actually quite a long way away from seeing Winston Peters or NZ First back in Parliament."
Mr Key believed he had made the right decision not considering a coalition with NZ First.
