Using noVNC to implement a web application?

I need to implement a desktop-like web application, and I'm considering "alternative" ways to go about doing this. The idea of implementing the app as a normal desktop app, then deploying it to the web using something like noVNC seems rather interesting.

What would be the major disadvantages to this approach? I think a big one is scalability. Each user running the app will essentially get his own process on the server, so if I had a million users at one time that's a million processes. And not only that, each instance of the application will need a corresponding VNC server instance. So that's 2 million processes. Of course, I don't expect that many concurrent users. But it is something to consider.

Is there anything else?