If we do that then we gain speed because it's faster to load PHP than to unserialize arrays and we win free of circular dependencies because PHP storage is independent of CMI (unlike the database based cache). We can dump objects that have get methods so that the language override is built-in. Lots of possibilties.
The challenge is mass hosting. Remember, we do not want PHP in a shared directory. The container allows for local storage because it can be rebuilt and the enabled module config triggers a change. However, now that I think of it, you can store php in memcached or redis and read via a stream wrapper. Just ideas.