One sticky wicket with the whole Charter challenge idea is that it would effectively preclude us from choosing a flavour of PR with a "cut off", or similar.
Once it's about "everyone's" Charter rights, we can't start clawing those rights back in order to have a system that we feel will be more efficient, or whatever. In other words, we could only realistically have a mathematically pure system, or else it would be the proponents of a cut-off who were denying some group of voters their rights.