It turns out the perfect OS already exists: Inferno OS [1]. It doesn't need a MMU and runs with less than 1 MB of RAM. I did not dive into Limbo yet but at first glance it looks rather sane.
I think “remote resources are files” paradigm has been definitively attempted and rejected.
At its heart it’s a lie: network resources are not files. They are not yet in RAM.
Unifying two abstractions into one is great, IF the data behaves in a perfectly analogous way. Otherwise the “unification” actually makes the domain of interaction more complex.
[1]: https://en.wikipedia.org/wiki/Inferno_(operating_system)