tl;dr: might be more-than-usual queries about how things work from users.
You can follow the work in bug 1463209.
I’ve notified Heroku users of the change, and a number of questions have come up that I’ll be redirecting folks to this forum to get answered.
FWIW, Heroku will require 2FA verification (not sure that’s worded properly), which aiui limit “linkage” to certain other services. (E.g. FxA & GitHub)