Too Long; Didn't Read
Microsoft introduced default interface methods in C# 8.0 in September. The new feature will enable many scenarios that were previously difficult or impossible to achieve. They mostly behave like virtual methods in an abstract class. This makes all the difference when it comes to code reuse, a.k.a. the Don't Repeat Yourself (DRY) principle. The approach is also very non-intrusive and won't conflict with existing code, which means it will be easy to slowly adopt it.