What still requires stock Android and has no alternative way to access?

I'm about to degoogle my stock Android phone. For the past few years, I've used it to handle the non-open source apps that I don't want running on my main phone. As I've finally weaned off GApps, I realize that I might as well go degoogle the rom as well.

edit: to be clear, I'll be using sandboxed Play services on GOS

But since that phone is my compatibility guinea pig, is it likely I'll still run into an app that demands unmodded Android with no alternatives? In your experience, has any bank or other service required the app on regular Android, with no alternative for the desktop, browser, etc?