1. Multimethods simply are a rare feature in general.

2. Multiple dispatch and static typing are completely orthogonal features.

3. Strictly speaking, you don't even need multiple dispatch. The key feature of multimethods that you need is the ability to add a method outside the class body.

under definition 3 then extension methods are also multi-methods - doesn't seem right. even c# has extension methods

Extension methods do not support dynamic dispatch and hence are not proper instance methods. Try MultiJava's open classes for an approach that works.