Former Wales flanker Martyn Williams says it would be a mistake to split an expanded Pro12 into two conferences.
Swansea council is in talks with Swansea City football club, Ospreys and Swansea University about the project.
Pro12 derbies would be protected if the league splits into two conferences after the arrival of Cheetahs and Southern Kings.
Former players praise "astonishing" Alun Wyn Jones as he prepares for ninth consecutive Lions Test.
Audio & Video
Former All Black Justin Marshall would have chosen Ospreys flanker Justin Tipuric rather than Sam Warburton for the British and Irish Lions' second Test against New Zealand.
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What's on BBC Sport this week
This week's sport on the BBC includes The Open, the conclusion of the Women's Cricket World Cup and action from the World Para-athletics Championships in London