Interesting connection with the term step-father, Sour, that makes a lot of sense. I agree that we need to redeem the inherent honor and respect of the role for those who choose it, and that's about way more than the word. It's about education, mainly. And it will, very much so, be different for every situation.
My concern is just about whether or not "secondary" gives people the wrong idea from the very start (note those less than cheery dictionary and thesaurus connotations versus "step" which doesn't really mean anything), and whether there's terminology that would be just as clear but wouldn't cause people to immediately think "less worthwhile."
A different term may or may not be called for, but I wanna see what we can come up with it. After all, ALL our terminology is so new, why not play with it?