While extensions must conform and not interfere with core specification, can different extensions interfere with each other?
If John Gruber is correct, it will be impossible to have a full commonmark that can cover all use cases.
Maybe extensions interfering with each other is inevitable, but at the very least we can group extensions together like coder, academic, law, etc… and mandate that within each group it must work together, but it is not as much of an issue (tho discouraged) to interfere with other extensions in other group. (e.g. An extension syntax for coder may interfere with film script)