Well, all things being equal a cleaner and more understandable language is going to be easier to implement, so I don't think difficulty of implementation should

Well, all things being equal a cleaner and more understandable language is going to be easier to implement, so I don't think difficulty of implementation should be dismissed so easily. Especially when the difficulty of implementation is not due to advanced features such as a fast runtime, resumable exceptions, proper tail calls, multi-method dispatch, pattern matching, powerful concurrency abstractions, SMP...