gistfile1.cs

var type = Class.New(new[] { typeof(ReactiveScreen), typeof(IHasState) }, cls => // Inherit from ReactiveScreen and implement IHasState.
{
  var state = cls.Field<IObservable<string>>(); // Default to null.

  cls.Property<IObservable<string>>(Modifier.Public, "State")
    .Get(Modifier.Public,  ()      => state.Get())
    .Set(Modifier.Private, (value) => state.Set(value)); // TODO: INotifyPropertyChanged support...

  cls.Function(Modifier.Public, "GetRandomNumber", () => 4); // Chosen by a fair dice roll. Guaranteed to be random.
});

Activator.CreateInstance(type);