Paul Wells highlights the major change from the Cons' messaging in 2011 compared to today, as the party which spent years doing nothing about obsessing over (and demonizing) the possibility of a coalition has suddenly gone mum except in front of the most partisan of crowds. But it's worth noting that there's another factor beyond those mentioned by Wells which might explain the change - and it involves the message backfiring to some extent the first time it was used.
Wells notes - as confirmed by the polling set out here - that even at worst, roughly half of the Canadian public supported the prospect of a coalition to oust the Harper Cons. And that held true through the 2011 election campaign - even though the governing party was using all of its resources to attack the idea, the apparent default alternative did everything in its power to repudiate any cooperation, and the only strong defence of a coaltion came from a party broadly perceived as an afterthought.
By the end of the campaign, of course, the NDP was seen rather differently. And its success in convincing voters that a willingness to cooperate represented change for the better (rather than some abomination against the inherent nature of politics) forced at least some observers to recognize that discussing a coalition wasn't so toxic after all.
Unfortunately, the Libs still haven't learned their lesson. But if the Cons are no longer pretending it's a winner for them, that's probably an admission worth noting - and it likely signals an opportunity worth taking not only for the opposition parties, but also for voters primarily concerned with replacing Harper.