Preliminary results of the community survey indicate that almost no users are using Rackspace compute resource. Additionally, the fog-rackspace gem which we rely on hasn’t seen a release in nearly two years, so it most likely is not compatible with the current version of fog-core. This means that most likely it is already non-functioning for at least several releases.
I suggest marking it as deprecated in Foreman 2.0 and dropping from core in 2.1. If there are people still interested in using it, we could extract it to a separate plugin, but otherwise lets just remove this (likely) dead code.
Issue for tracking this effort: Refactor #29284: Remove Rackspace from Core - Foreman