Also what about deployments/bug fixes? Seems if you need to make changes to the html fragments you'd have to do a full app deploys every time. Versus making changes to specific JS file and uploading it.
Personally that's why i like this whole shift to single page apps. Just as we've decoupled certain aspects of the server-side development, we can do the same with the UI.
Seems it's a highly refined version of what was done in the "old" days. I remember doing something similar for an old project in ASP.NET. (Well more similar to pjax)
As to performance on mobile, i think it might all depend on how large the html fragments are.
Personally that's why i like this whole shift to single page apps. Just as we've decoupled certain aspects of the server-side development, we can do the same with the UI.