McGeechan and former UK Sport performance director Peter Keen have been commissioned by the RFU to come up with a blueprint to improve English rugby at international level.
McGeechan said: "There is an argument, and I know people disagree with me, that if you want rugby to be the best product then you don't have relegation."
He added: "If you want club rugby to be the best business then you give it time as a business to establish itself. It may not be just 12 clubs, if there are 14 or 15 clubs that are set up to be professional in the right way why not make a 15-club league?"
His ideas on club rugby will not form part of the review but McGeechan - the former British Lions and Wasps coach, now chairman of Leeds Carnegie - believes removing the fear of relegation for five years could revolutionise the club game for the better.
He believes it would allow clubs to draw on the advantages enjoyed by the Super 15 sides in the southern hemisphere.
He added: "Then there would be no reason not to put the best product out on the field and that is one of the advantages the Super 15 has."
McGeechan said the fear of relegation often contributed to Premiership games being too negative.
"The nitty-gritty of the Premiership is that it is a tough competition. Speak to some of the southern hemisphere players and it is the toughest competition you can play in because week in and week out you are working very hard to win games and it is very competitive," he said.
"Remove relegation for that period and that gives five years for Championship clubs to get the model right and have the right facilities and infrastructure if they want to be a Premiership club. Or if you keep relegation, have the bottom club playing off against the top club in the Championship."