Cannon to me is FS1/Silent Threat/FS2 + any possible Future V product, that's it...
As for alternate cannons? Each campaign out there already is. They don't need to be validated by a new term. I do think it would be neat in the future with willing people to have props shown to previous campaigns and tie them in to later ones with some storylines (that way we can have a truly LIVING FS history). While not mandatory, I do thik it's a neat idea. It would be up to each future mod team if they want to pick up any past storylines/events and expand on them (with permission if it was from a user campaign, but fair game is it was a FS1/FS2 game thread no one has explored yet)... Lets see how creative people can get story wise (I enjoy good missions as well as new "toys")
Plus I don't think I could stay in teh box of "cannon" material. What grabs me the most is alternate interpretations of teh past, or Cross-genre games.