OP this sounds like a cool idea, but it would mean rolling out 8 more classes. Even if added slowly it would be a rather huge task and comes with a special con: it would negatively impact sales.

A move like this would lessen the excitement and mystery about what class we could get. Instead of "oh man we just got GNB, Sage, and Reaper! The gate are thrown wide and we could get anything!" It's, what jobs are like the ARR ones they haven't made pairs for yet?
Considering how much emphasis they put (and are made to put by sales and upper management) on the excitement of new jobs to help sell expacs, I don't think we can expect them to do something that would compromise this excitement and the sales potential for multiple expacs to come.

It is a very lovely idea and I'd like to see it happen. But... I wouldn't bet on it and I don't think anything shy of unanimous community support (which is a pipe dream in and of itself) would make them consider changing their minds : (