You may want to read the article “The Right Place” by Lee Eisenberg in the May 1981 issue of Esquire magazine, about how leading edge members of groups (dream-chasing scouts, he calls them) select the next hot place to migrate to, in this case Santa Fe New Mexico.
Dream-chasing scouts are the vanguard of Creative Class migration. They move to Portland, Oregon before anyone else knows it is cool. I would call it a "pioneer migration" and I'm sure there is some academic term that defines the concept.
There you have it, Rust Belt outmigration. Now I need to figure out if it is a "stream".