So, a few thoughts on this. One of the advantages of Ionic is that you also get a mobile app for the app stores out of it. That's something that Flipkart wouldn't get, though they would get a desktop codebase. So, maybe that's a wash but it is more that one gives you one thing and the other gives you something else.
That being said, we are starting a serious effort to add desktop and tablet support to Ionic, so in the near term we expect to have Ionic deployment to native app (tablet and mobile), PWA, electron, and desktop app.
As for auth, there are a few ways to tackle that. First, Ionic apps can just use any auth API (oauth, JWT, etc.), and many web apps are built with this kind of authentication. If not, it's not going to be a big effort to add traditional session/cookie auth to an Ionic web app and to easily render these apps with server side rendering. We don't technically support that yet but it's something you get from Angular and Angular Universal with Ionic is going to be something we push in 2017.