On Monday, all three countries were drawn together in the toughest pool of the tournament, with the likelihood that they will also be joined by Fiji as Oceania qualifiers.
The Millennium Stadium was included in England's original bid document and debate has raged as to whether Wales should be afforded home advantage for any of their major pool matches.
While England may not play all their pool matches at Twickenham, it seems inconceivable that Stuart Lancaster's men would be ordered to play against Wales in Cardiff.
But tournament organisers England Rugby 2015 have refused to rule out the possibility that the host nation may have to go to Cardiff for a crunch pool fixture.
WRU chief executive Roger Lewis said: "It is very important to remember that Wales was included in the England bid for matches in the Millennium Stadium.
"What was pencilled in (for the Millennium Stadium) was eight games and the Welsh government and Cardiff city council would provide financial support to the tune of £1.4million.
"The UK treasury supported the under-writing of the competition and of course, Wales is still part of the United Kingdom.
"We would be very welcoming hosts. The discussions will now begin.
"I think they (England) would embrace the opportunity to play in the finest rugby stadium in the world.
"I think everything must be up for discussion because it is the finest rugby stadium in the world."
ER2015 will spend the next three months piecing together the fixtures and the venues before announcing the final schedule in March. The Millennium Stadium is one of 17 venues on the long list.
"Roger has invited us, which is very kind of him. I am not going to say one way or the other," said ER2015 chief executive Debbie Jevans.
"At this point I am not ruling anything out an I am not ruling anything in.
"I understand where Roger is coming from. He is pushing for as many games as possible to be in Cardiff. I don't hold that against him.
"Now we know what the draw is we can go away and look at the appropriate venues for the appropriate matches."
The England team management can make representations but they have no input into the final decision, nor do the Rugby Football Union despite being tournament hosts.
The ER2015 board will draw up the final fixture schedule, including the final venues list, which will then be rubber-stamped by Rugby World Cup Ltd.
But red rose captain Chris Robshaw made plain his desire that England should be at Twickenham, where he led his country to a record 38-21 victory over New Zealand on Saturday.
"Of course we want to be at Twickenham and have home advantage - 80,000 people shouting you on and cheering you on," Robshaw said.
"We speak about the power of the nation behind us and we definitely felt it on Saturday. If we can get to those standards it will be great."
The ER2015 announcement in March will also include confirmation of the opening fixture on September 18, which is sure to be at Twickenham.
Australia, England and Wales will be joined in Pool A by the Oceania qualifiers - strongly favoured to be Fiji - and the repechage winners. In 2011 they were Romania.
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