The more low-level access browsers are required to expose for application development, the worse things will be in almost every dimension, but especially security and performance.
I'm curious, how does adding notifications effect security negatively exactly? Performance?
All this functionality is already available for apps including the security model. Nothing new is happening here. App security is an issue, but it's one big tech is already dumping resources into solving.
But, frankly, browsers have some of the best management features for culling analytics, telemetry, watching the traffic and requests being made. It's many times easier for me to see what a web app is doing on the network, and write something to stop it, as compared to a native app.