Abacus' latest federal poll includes some noteworthy data on which voters see a real prospect of shifting their preferences - and particularly on the number of voters who are willing to entirely rule out a vote for either the Cons or the NDP.
In particular, Bloc and Lib supporters are roughly twice as likely to say there's "no chance" of their supporting the Cons than the NDP (72%-37% and 50%-24% respectively), while the Greens aren't far behind at 52%-30% - all of which suggests that plenty of non-supporters are somewhat leaving open the possibility of uniting behind the NDP as the leading alternative to the Cons. And even comparing the parties' own supporters, more NDP than Con voters rule out a vote for the other party by a 63%-56% margin.
Which leaves one noteworthy group of voters where the Cons point to a slight advantage in growth potential: those who are truly undecided, who rule the Cons out slightly less than the NDP (43% compared to 48%, with a comparable advantage in respondents indicating a "fair chance" of support).
Now, I'd be interested to find out what group of voters is mostly represented in the "undecided" group to produce that result. (Perhaps Red Tories and blue Libs who aren't currently satisfied enough with any of the options to indicate a preference?) But it's noteworthy that the NDP looks to have far more room for growth than the Cons among every other party's supporters - meaning that the Cons' hold on power may depend on their being able to reach voters who haven't yet found any reason to support them, rather than merely catering to their current base.