Let's suppose that Cullen's proposal comes to fruition. Let's also say that in a particular constituency the Liberals and NDP are each fielding a candidate for joint consideration. What's to say the candidate who loses won't say, "%@!@#%$ it, I'm running as an Independent anyways?"Yep. And how well do independents who aren't incumbent MPs or hosts of highly-rated talkshows do? Even most incumbents who lose their party's nomination get defeated running as indepdenents.
Would all the parties be able to transfer 100% of their votes to the joint candidate? Of course not. Would the consensus candidate get significantly more votes than in open competition, you bet.
Ask Niki Ashton if Bev Dejarlais's decision to run as an independent affected the outcome of that race.