My concern is for content increasingly being siloed within an app that only permits its use in ways encouraged by the author. An IDE is a decent counter-example, since nothing like it would have been feasible before js apps began displacing the web. But it's more and more unlikely that any app other than that IDE will be able to access your source code, simply because it's easier not to bother supporting a stable and documented API when the maintainer's favored client can be revved at a moment's notice.