As another data point, IBM WebSphere had an open-source version and a paid version which used AspectJ (AOP) to deploy proprietary features. People could deploy something like that potentially even at runtime via remote libraries and load-time weaving. (The technique was called product-line engineering.) Obviously Spring still does something similar with its AspectJ-derived AOP. It works mainly for features applied as transaction/API filters like authentication, security, first-failure data capture, etc., and when OS is used as an training tier rather than a fallback if the company folds.