Third party browser & JavaScript engine + ability to install web apps on the Home screen = third party app store that doesn’t have to pay Apple’s fees.

When Apple could force everyone to use Apple’s WebKit, web apps didn’t matter as much as Apple could limit WebKit features to push people to the App Store. E.g. it took ages to get push notifications on WebKit. If Google and Mozilla are free to make whatever improvements to their browser engines, the need to have native apps on the phone decreases considerably.