"Some leaders are very much of the view that it is a foundation stone from which new entrants should be allowed to join so long as they meet the standard.
"Others took the view that maybe we should let it settle down a little bit first.
"But I would have thought if you can meet the standard, myself, I cant see why you wouldn't let other people in."
Asked whether the US was one of countries that wanted to let things settle down before considering new entrants, Mr Key said he thought the US was open-minded about it.
Trade Ministers are going to work on a proposed protocol for new entrants.
Several countries have already indicated an interest in joining including Indonesia, the Philippines and South Korea.
Mr Key said Mr Obama turned to him next after he had spoken which was a sign the US saw New Zealand as having "pushed the process and New Zealand being a leader in trade."
The ceremony would showcase New Zealand as the place where the biggest free trade agreement was signed since the Uruguay round of the World Trade Organisation.
The deal cannot be signed before February 3 which is the end of the US Congress 90-day review period of the deal.
Mr Obama made a few opening comments to the meeting in public and said he wanted to ensure it was enacted as swiftly as possible.
"Obviously execution is critical after we have arrived at the text and I just want to once again commend all the leaders here for their extraordinary leadership .
"This is not easy to do. The politics of any trade agreement are difficult.
"The fact that everybody here stepped up and made some hard decisions that are going to pay off for decades to come I think is a testimony to the vision that was reflected."
Earlier yesterday, Mr Key has a bilateral meeting with Chinese President at Xi Jinping's hotel - and trade was on the agenda too.
They talked about possible negotiations to upgrade the 2008 New Zealand China Free Trade Agreement - its first with a western country.
But the upgrade, in the wake of other deals, is not an absolute certainty.
"We are as confident as we can be on the basis of the discussions we have had so far it is going to happen. But for an upgrade of the FTA to happen, we have to formally launch that process and work our way through that."
New Zealand was very keen to do that and China has acknowledged it would make sense to occur.
"At this stage the officials in China haven't formally ticked that off but the Preisdent's comments were forward-leaning so I would have thought we are going to make progress there. That is my sense of it but you just cant guarantee when that process starts."
Mr Key said Mr Xi gave him an update on the Chinese economy and said the while growth had slowed, it was from a large base.
Mr Xi had predicted that China's economy would grow by $US800 billion this year.
"His basic point was that was bigger than a medium-sized economy. It was about $700 billion last year. His main point was that there was still huge consumer demand."
They discussed the territorial disputes China has with five countries in the South China Seas and the reclamation China is undertaking to enlarge an atoll and build airfields.
"He just said they had the right to do it because they believed it was Chinese territory and they were doing some work there but his basic point was there is nothing to be concerned by that."
Mr Key's bilateral with Mr Xi was held at Mr Xi's hotel, a down-market hotel compared to the five-star hotels of other leaders, but one owned by a Chinese-Philippines businessman and chosen by the Chinese.
So down-market was it that the New Zealand Foreign Affairs Ministry official accompanying journalists rang officials to get the right address, assuming she had been given the wrong address.
Since Mr Xi has assumed office he has been on an anti-opulence campaign.
