Most of Web Apps are already in the standard (appcache, indexeddb, etc.) and I know there has been some communication around manifest formats (but I'm not directly involved in that).

Generally speaking, though, the difference between one definition of "web app" and another is very small, in terms of what the platform has to support.

I'll also note the perspective that sometimes it takes a couple of implementations before the "right" solution is known. Many evolutions of the web standards have followed varying implementations being played with in the field.