the risk of incompatibility of the kernel 

the heavy integration that is done once at the end of the process

the risk of inability to integrate an increment

SAFe is used for the coordination between multiple scrum teams

SAFe is used for planning the global view of the work without going into details

SAFe is used for planning the detailed substories of scrum

SAFe ensures safety of the scrum development process

An interface defines behavior without implementation

An abstract class supports multiple inheritence (in Java and C#)

Abstract classes can have both abstract and concrete methods

An interface supports multiple implementation

Abstract classes cannot have implemented methods