Will we still have to wrap Safari Extensions inside a macOS app? I don't have a macOS app. I just have an extension I'd like to bring to Safari in the same way I have for Chrome, Firefox, and Edge.
Yes, Safari Web Extensions need a containing Mac app. The xcrun safari-web-extension-converter tool in Xcode 12 Beta will make a Mac app for you. This tool is covered in Converting a Web Extension for Safari.