Teams with cap space next year:
Boston, Charlotte, Cleveland, Denver, Golden State, Houston, Indiana, Minnesota, New Jersey, New Orleans, Orlando, Philadelphia, Phoenix, Portland, Sacramento, Toronto, Utah, and Washington.
A lot of those teams probably wouldn't want Marion, but some would. And I don't think the list is as limited as you do, because of the higher salary floor, plus a lot of teams being delusional about their odds. There's also the possibility of a cap room team accepting an expirer from an over-the cap team(to meet salary floor requirements), with Marion then going to the over-the-cap team.