Needless to say, it's disappointing that there now doesn't seem to be any prospect of a shift to a more proportional federal electoral system without a referendum. But the NDP's move to build a consensus among the opposition parties on a referendum offering a choice between mixed-member proportional representation and first-past-the-post makes sense given the apparent alternative.
After all, the Libs' surprise mass mailout on electoral reform could only have been intended to set them up as the sole arbiter as to public preference. And they've surely already written up their talking to the effect that if one squints just right, the steady stream of "we want PR!" received in response could be interpreted to mean "we want whatever Justin Trudeau sees as best for his own career prospects!".
That left multi-party cooperation as the only possible counterbalance to the Libs' attempt to take full control of any decisions. And while acceding to the Cons' desire for a referendum in exchange for agreement on PR as an option leaves open the possibility of a broken promise to end first-past-the-post (while also creating all kinds of logistical questions), it at least leaves the best possible reform on the table based on public support.