They're going to heavily lockdown WKWebView after the Instagram and Tiktok revelations, probably in iOS16.1. They may even remove it entirely and force people to use SFSafariViewController (heavily locked down web browser, opaque to developers other than URL). Best of luck to anyone that was using javascript injection for legitimate purposes, others have ruined it for everyone by abusing user trust.
I expect app-bound domains to become required for all apps in iOS 16 or possibly iOS 17. There will probably a be a limit and some review on which domains an app specify as app-bound. Web browser that use WKWebView already have a special entitlement that excludes them from this.