The browser turning into an operating system (or rather a separate meta-platform that provides a common wrapper over operating system services) has already happened a long time ago.

And while many web APIs indeed 'suck', they're still roughly in the same ballpark as traditional OS APIs when it comes to legacy features, unfixable design warts and general 'pain of use' (e.g. it's not like native development is all rainbow-farting unicorns, while web development is eternal pain and suffering - it's both 'mildly annoying' most of the time).