Imagine for a moment that BC's core modules were in fact built on the web app engine. Not the web app engine as we see now, but an enhanced one. BC could lock those modules/apps so their core aspects are not editable, and then they enable them for their appropriate hosting plans. Those would simply be mechanisms built into the system.
Then, if someone wants the ability to create their own version of one of the modules (by building an app, not by editing the existing module), or they want to extend them with web apps, they have to be on the higher plan.
Not swaying this vision, Liam. It's too thought out.
In the long-run, it would make for an easier time for BC maintaining the system as well. Instead of working with all these different setups for their different modules, they would simply be using, enhancing, and fixing one framework. They could even benefit from what partners build, as they would be using the same technology.