The ability to build a solid backend platform and infrastructure is going to be increasingly important in the future. The "backend" is becoming increasingly anonymous (as in not seen, not as in privacy), but it has never been more important.

If nothing else the increasing focus on data collection and processing will push the need for custom backend forward for many years. Any every application that needs to store or share data via an API, needs an backend that understand the data it receives so that it can validate, process and distribute that data correctly.

Backends (custom backends) aren't going away any time soon.

Your question reads as if you believe that "backends" equals desktop applications. Even in that case it's still hard for web application to compete with desktop applications. It's a matter of personal preference of cause, but something like Google Docs feels weirdly restricted, confined and cramped somehow, simply because it lives in the browser.