Why use Type.FullName? It is without assembly name.
in ReactiveUI.Routing/RxRouting.cs you use Type.AssemblyQualifiedName and incorrectly (I suppose) convert it into interface name. Then you use Reflection.ReallyFindType(ifn, true); It will always work incorrect!!! 
Because Type.FullName and Type.AssemblyQualifiedName is not the same. These strings are not equals even when types are equals. It is bug. Or may be i don't understand something.