The title uses the word "coalition", but really the argument speaks to more of a "non aggression" pact between the Liberals and NDP. No secret to anyone, the Conservatives benefit greatly from a divided center-left vote, as the professors argue in the piece. The idea of the Liberals and NDP agreeing not to run candidates where one or the other could win, minus division, has obvious merit. Whether any talk is practical, given entrenched self interest, remains to be seen, but it's an intriguing proposition.
I did some digging on my own, using the 2008 riding results, which does present a huge potential, if people looked beyond their narrow partisan perspective. Quantifying all ridings where a Liberal or NDP finished second to either a Conservative or Bloc MP, you see the absence of the other could have tremendous impact.
The Liberals finished second in 107 ridings, the NDP 53. What I found surprising, just how many of those ridings were close enough, that the elimination of one party would probably flip the seat. Many of these second place considerations are mute, given the landslide percentages for the incumbent MP, but a large percentage are not. A healthy percentage of NDP second place numbers include very distant totals, wherein any agreement would have little effect. A general thesis, the NDP clearly hurt the Liberals, more than the Liberals hurt the NDP, which in and of itself probably isn't attractive. That said, any agreement would increase NDP seat totals, relative to no arrangement, so there is a self interest consideration for both parties.
In the last election, there were 35 seats where the Liberals were within 10% of the Conservatives. Everyone of them would flip, if the NDP candidate wasn't present, and one assumes were that vote would largely move. That is just the starting point, because a quick review shows many more seats in play, if the Liberals and NDP weren't competing, to the advantage of the Conservatives. If the two parties simply agreed to not run candidates where they have no chance of victory, Stephen Harper would be gone, it's as simple as that.
Back to reality for a second, the major obstacle to this proposal, beyond partisan interests- our public funding system virtually negates this possibility. Parties receive money based on votes, which means not running a candidate is counter productive. Hard to believe the NDP would agree to a disproportionate "stand down", because even though they would win more seats, their vote percentage would fall and the coffers would suffer. For the Liberals, a deal is less offensive on this score, because they are an almost non factor in the majority of NDP second place ridings. Any loss in support would probably be made up by cultivating NDP votes in those ridings where they didn't run. Almost a wash for the Liberals, a decided disadvantage for the NDP overall.
Philosophically, an agreement has a "no brainer" quality, if people are truly interested in seeing a center-left dominated Parliament. The NDP would hold the balance of power, the Liberals would be in government and Stephen Harper would be gone. However, while I find that scenario attractive, you can see how any such talk would be quickly derailed, primarily because the idea necessitates a "greater good" mentality, and that is more wishful thinking than practical probability.