As long as the feature doesn't exist, people have to make websites that work without it. As soon as it does, people will instead switch to obnoxious interstitial screens telling and/or insisting that you enable push notifications or whatever to continue using the thing.
Apple's not going to just drop in a change that makes you go through popup and notification hell.
I'm 100% certain Apple would give users control to enable or disable features on a per site/pwa basis.