This whole file has been one strategic blunder after another for the Liberals. 

Trudeau made a clear promise and earned a clear mandate. They should have simply introduced ranked-ballots as a normal change to electoral rules and let the chips fall where they may. 

But no, they blinked and consented to some further vague consultation, openning the doors for what no-one wants, PR and now stuck with no rationale for not going for a full referendum. 
At that point they should have offered ranked-ballots with a yes/no referendum and let the chips fall where they may. 
Now they have broken a major promise and look like donkeys. And worse yet, the original promise had a built in 'bring forward' date: election time! 
The Liberals were hoist on the petard of being too-clever-by-half, but gutless.