This could soon become very interesting, because, if it's sustainable (still questionable) and the Lib Dems came first in the popular vote, they would probably still end up only the third largest party in the Commons. If that happened then PR will be inevitable, after all, none of the other parties could win the argument that the system produces an equitable outcome.
So, let;s play a game for a second, imagine the Lib Dems won the popular vote but were the third largest party. Would we perhaps see a very short Parliament that produced just one law change, the introduction of proper PR along the lines of the Single Transferable Vote, and then a quick dissolution and General Election under the new system?
Given the Teflon-coated behaviour of politicians since 1997 and the complete apathy of the British public, what makes him think that whoever wins would give a fuck about "winning the argument that the system produces an equitable outcome"?
Dizz, baby, I don't know if you've noticed, but our politicians don't give a flying fuck what we think.