PDF.js allows for an inline/controlled display of a PDF, where you can control the interaction in a browser. Given, this is of limited use, and there are other solutions.
That said, the browser will not return to only acting as a display conduit with no interactivity despite what some people would like to see...
If you want a better platform than the browser for server-driven interactive applications not requiring you to install extra applications, then build one. To date, there hasn't been a better, more open option.
The stronger argument for pdf.js is that you get to leverage the Javascript sandbox instead of having to sandbox a native code binary (or worse, support a plugin interface and hand over the keys to the system).
That said, the browser will not return to only acting as a display conduit with no interactivity despite what some people would like to see...
If you want a better platform than the browser for server-driven interactive applications not requiring you to install extra applications, then build one. To date, there hasn't been a better, more open option.