This is backwards. Developing for the web has become a de facto standard because it's the only thing that's universally available. It's the best you've got.
If you want a good universal app platform, we should go all the way back to having something like the JVM as the standard. Or just like, browserless WASM, if we're thinking incrementally.
You might be able to get a headless JVM running on the web using the LLVM backend in Graal and the WASM backend for LLVM.
One thing that's missing seems to be tight integration of the UI aspects, for anything significantly advanced you're going to at least be waiting for WebGPU, and even for ordinary examples cross platform consistency is non-existent.
As someone who used a WebOS phone, the software was excellent, but the hardware was a little less. I had two different phones-- a Pixi which had a dead earpiece/speaker from day 2, and a Pre. The latter was an odd form-factor, and apparently prone to twisting apart on the slider mechanism. Neither were performance kings and the screens were tiny even for the era.
If they had put the software in the hands of someone who knew kit-- a Samsung or LG or even Nokia instead of Palm and eventually HP-- maybe it would have competed better.
If he meant a phone OS that only works with internet, that is a big no. XBox has already jumped the shark with this and other OS's like Microsoft Windows are slowly warming up the frogs in this direction.
If he needs a reason then require him to first get all his vehicles modified to iPXE boot. No internet, no go.
Like other commenters have said, there is KaiOS.
It's a rather neat environment actually - Firefox itself shipped with all the development tools and means to sync apps to the device. I wrote a simple IRC client for the Nokia 8110 4G, which has its very own hacking community (called Banana Hackers) and it was great fun.
However as those devices aren't that powerful, you really don't want it spend a lot of time deal with remote content/media.
That's all, felt like the right place to share this thought.
Well then you will need a Web browser. But 95% of Browser usage is Chrome + Safari. And Firefox with 90%+ of its revenue from Google.
Not to mention the Web, in terms of Tech sucks compared to Native. 10 Years later after the push from Facebook and Google, the best of HTML5 Apps still isn't as good as average Native Apps.
If you want a good universal app platform, we should go all the way back to having something like the JVM as the standard. Or just like, browserless WASM, if we're thinking incrementally.