Great question! By the way, sorry for the late answer.
The answer is no, there is no danger importing the same ES6 module multiple times.
The way how module import works prevent the evaluation of the same module multiple times. Taking the code from the post as an example. The first time we import Vue, the browser will evaluate the module and all modules it is dependant on. Next time when we import Vue again the module won’t be evaluated and it will return the same instance of the module.