I only know detail about the iOS equivalent (https://developer.apple.com/reference/safariservices/sfsafar...) but I'm not expecting Facebook to implement it any time soon as it makes it a lot harder to track where a user goes (you can't access that) and/or inject content into the webview.

On the current Android and iOS implementations a user is far less likely to share on, say, Twitter, because they won't have their Twitter login cookies in the Facebook browser. I suspect Facebook is quite happy to keep things that way.