There are definitely a lot of nice spool holders / mounts available but I couldn't find one that met all of the criteria I was looking for:

1) Does not require any additional parts (other than wall anchors / screws)
2) Works with any size / type of spool without sliding or coming off
3) Rotates parallel to wall and sits as flush as possible
4) Allows free movement to prevent any filament binding
5) Minimal number of holes required to mount securely
6) Protects wall from scuffing
7) Can easily access and quickly replace spools

There are two parts - the spool mount and the spool cap. The cap is designed to prevent spools with a larger hole from slipping off and without having to waste time with threads or anything similar - it simply slides and locks into position. This design is intended to be highly functional and easy to print while maintaining simple yet appealing aesthetics.