[exabrial]

Simple: don't. Do the simplest possibly thing that can work. Only code for today's requirements. You can't predict the future. Creating extension points without a past pattern of data of how the system is being extended is just guesswork, not engineering.

Once you have a established a pattern of how the system is regularly extended, then you can use that to make predictions about the future. Keeping your codebase well-tested, small, and light will do far more to help you respond to change than guessing.