Solved! Go to Solution.
Deprecating interfaces breaks the COM contract so it will probably be there for the foreseeable future. The only time I saw esri deprecate interfaces is when they deprecated the class too. if you look at the classes that implement IFeatureLayer2 and compare to the classes that implement IFeatureLayer, you will notice not all classes the implement IFeatureLayer, implement IFeatureLayer2, so for those you have no choice. ArcObjects is littered with 2, 3, 4... interfaces for the precise reason that COM forbids modifying a published interface so if you have a compelling reason to use IFeatureLayer (maybe the method you want to use returns IFeatureLayer or takes it in,) then you are fine.