My suggestion
An option to evaluate JavaScript on specific pages which can be entered in the browser.
Why?
JavaScript is a pretty powerful language. The idea behind this is the possibility for developers to engineer “plugins” or “addons” to automate specific tasks on a webpage they visit regularly.
This could be as simple as applying some CSS so that Google will finally appear in dark mode or as complex as automating a file download on a specific webpage everytime you’re visiting it.
The result is great customizability and a huge amount of new options for devs.
And the best part is that implementation isn’t actually that difficult.
Since the WKWebView has native support to evaluate JavaScript you “just” have to write a good looking UI to enter the JavaScript and a way to trigger it.
PS
I’ve posted it in the iOS Thread since I‘m using iOS. The feature will be as great on Android as it will be on iOS and the implementation shouldn’t be any harder since the Android WebView is able to evaluate JavaScript as well.