What I mean by obsolete is that it is no longer the hot new thing on the bleeding edge of technology. I chose Django because it wasn't the hot new thing; I'm already familiar with it, I've written a half dozen sites using it, and a general rule when founding a startup is that you shouldn't compound market risk with technical risk. Right now, my biggest problem is building a product that users want; I want the shortest path toward getting the big things right, not the sexiest little things.

But Django is definitely showing its age, and the environment has changed in ways that make you work around the framework instead of with the framework. Users are getting accustomed to logging in with Facebook or Google instead of having a separate registration system for each site; this is available with django-allauth, but then what's the point of having a built-in authentication system? Users are increasingly getting accustomed to direct-manipulation user interfaces instead of forms; Django has no support for that, and newer alternatives like Meteor beat the pants off it in that regards. Users are shifting to mobile; Django mobile support is spotty, largely provided by a set of sparsely-maintained third-party addons.

And then there are new technologies that promise to throw a huge monkey wrench into the web development ecosystem. Polymer & webcomponents are coming down the pipe, quickly; they introduce the idea of an application as a client-side set of individual downloadable components, which means that a lot of Django's routing, form, and templating infrastructure is no longer relevant. The increasing use of storage options other than RDBMS (Redis, Mongo, RethinkDB, protobufs or JSON on disk) makes the ORM less useful. JS-heavy apps shift the focus from building HTML quickly to building bundles of related JS functionality quickly, and Django has no built-in features for that. The most common solution, Bower, is pretty heavily tied to the Node.js ecosystem.