In this article I've found text:
With secure paste, developers can let users paste from a different app without having access to what was copied until the user takes action to paste it into their app. When developers use secure paste, users will be able to paste without being alerted via the pasteboard transparency notification, helping give them peace of mind.
The question is will secure paste feature allow developers to restrict access to clipboard for another apps somehow (so it will be impossible to copy from pasteboard anything) or this feature is only that user not notified about paste in some cases now?