Since I couldn't put my two cents into the original thread, I should respond to where it left off: the relationship between parties and "labour."
The "social-democrats" lite of this forum would say that a party further to the left of the NDP would be divorced from "labour," which is ironic considering the attempts by the right wing of the NDP to do exactly this.
I think one of the factors toward this is whether such a party can have its own separate union, such as the All-Workers Militant Front affiliated to the Greek Communist Party. Another factor is whether left syndicalists can get their act together and realize the connection between apolitical syndicalism (not tying yourself to politics let alone parties) and abject failure (IWW).
Another factor not discussed in the original thread is whether the new party restricts voting membership to those of a working-class background. So, for example, corporate executives, lawyers, speculators, intellectuals making a living by selling books and academic papers, etc. would not be allowed to join this party.