If you don't want updates for whatever reason, just take an older commit of SN's front-end (it's open source) and connect it to the current API. Boom, you have a frozen frontend until it breaks because the backend changes (then you'll realize why auto-updates weren't necessarily a bad thing). Still don't need a native app.

The problem that you mention (styling articles) is a you-specific problem. Suppose you write an app that does that. But someone else doesn't want that, they actually want them a different color/font/whatever. Should they now write their own app or fork yours? The real problem is that mobile browsers have limited options for injecting custom styles compared to desktop (a PWA is a browser window sans the browser UI). Or, SN could just add an option to inject your own CSS.

Also, I'm surprised that you think going to an app store, finding an app and installing it is better experience (and easier to walk someone through that) than visiting a link and clicking an automatic prompt to install.