The problem of web apps on mobile is not that they don't work offline. They've worked offline for years with appcache. The problem is three-fold: (1) performance is bad and not improving, especially (and paradoxically) on android, (2) lack of native controls produces an inferior ux and (3) you can't store more than 50 mb of data on iOS.

I was gung-ho on the mobile web as app platform and was sure that it would beat out native on mobile as it did on the desktop, but the situation is different. Web apps have a worse install experience on mobile, taking away much of the reason to build for the web, and because there can't be competing browsers there is no competition between browser makers to improve the mobile web, keeping it in a pretty lousy place.