The Cliff's Notes version of the discussion of the first appearance of Big Hero Six from the thread dedicated to that group:
The creative team of Alpha Flight had an idea for a bunch of new characters to appear in that book a few issues down the line.
The higher-ups in editorial liked the idea and decided they wanted to do a mini-series with the characters.
The creative team of Alpha Flight did not have time in their schedules to work on the mini-series, so the book was given to another creative team.
The first few issues of Sunfire & Big Hero Six were published.
Later, the issues of Alpha Flight (the issue with the cameo and the full appearance) were published that included those characters, on time, without delays, when those issues were intended to be released according to the publishing schedule, after Sunfire & Big Hero Six.
Years pass during which no one cares about the characters and Disney buys Marvel.
Disney announces the Big Hero Six movie.
A thread starts here that includes a discussion of the first appearance.
Divad sells an issue of Alpha Flight with a description that clearly designed to inflate the importance of the issue.
Very, very well done sir! Short, sweet and to the point. Now, which one do I speculate on again
The issue of Marvel Vision that has an advance promo.
Bah! I will forego all previously provided excellent information and buy a 1st edition Blu-ray of BH6 upon release. Then I'll know that I have their first appearance in a movie.
Right?