I suppose the closer the browser gets to just being an operating system running in a pseudo-virtual-machine the less crappy the non-desktop-experience will become. On the other hand we're already approaching absurd levels of JS required as a download for some web sites. I could easily envision, in some dystopian future, a scenario where hundreds of MB (compressed) of JavaScript or more are required for an especially loathesome resource eating web "app".
Is it really better to have to download 10s or 100s of MB of JS every time (yes, yes, caching helps) you want to use an application instead of a one-time install of a couple of GB?
Edit for clarity: I'm responding to the part of your comment about web apps "eating" the install-based model of desktop apps, specifically, not to the broader topic of mobile apps (as clearly there's a difference in the model, packaging of applications, etc. there).
JS isn't nearly as offensive as those exaggerated numbers by comparison
Nothing more irritating then being forced to update / download content when you need to go and quickly do something in an app.
No- the crappier your computing experience will become, which is already happening.
However there is significant effort being made in making these browsers better, so perhaps something will improve.