Current behavior:
Mock.Arrange(xxx).IgnoreInstance();    //mock all future instances of the type on which I set an expectation.


Feature Request:
Mock.Arrange(xxx).IgnoreInstance().Next();    //mock the next instance of the type on which I set an expectation.

...and even better...

Mock.Arrange(xxx).IgnoreInstance().Skip(3).Next();   //mock the 4th instance of a type on which I set an expectation.