Some implementation that allows for browser level customization(timing, etc), as well as a notification center in the browser, and that integrates well with screen readers.
I like toasts from a visual perspective. They can look good(not always, of course), and they can convey small bits of information that could otherwise be displeasing to view in some designs. However, god have I missed a ton of notifications because of them disappearing too quick, and no way to view previous ones, or anything like that. I'm not visually impaired or anything, so I can't really comprehend the extent and issues people who do may have with toasts, and see what would be needed to make them accessible for them(if it's even possible), but would love to hear about it.