The idea is actually just not that. Because, by doing this, you will really soon be limited by the ressources of the computer as it will have to run a complete game engine multiple times, in addition to a local server. That will completely kill the perf of the computer.
The idea is to create a new window, a new OpenGL Context, and then in that window, run a new Viewport node. Like that, there is actually no other instance of the engine running, and information will be shared faster and easier, and the processor will be less busy. That would allow the game to use more ressources in its graphics, AI, or gameplay.
Your solution is probably the laziest, and the quickest to implement. If someone has a light game and the need for 2 or 3 windows, it would work well. But I am more into performance, and I do not see how to link a new Viewport node into a new window...