Everybody wants the OS to be easier for THEIR use case, underestimating the diversity of computing. "Why can't I just have a whole OS in node.js, e.g. https://node-os.com/ ? That's all I need."
Well some people need to run linear algebra on computers and don't have any need for that stuff. Likewise you don't have any need for Fortran.
The "language as OS" thing has been tried with Lisp and Smalltalk, and failed to gain adoption for good reason. They are both just languages now.
Microsoft already tried and abandoned the second idea (WinFS). File systems are complex, but databases are an order of magnitude more complex. OSes evolve on a slower time scale; databases and languages on a relatively faster time scale.
Multiple databases are also a feature. Both sqlite and Postgres/MySQL work on top of the file system. The file system supports the minimum API you need to write a database. (It's somewhat bad, but the way to fix the API isn't to replace it with a database)
If you had bundled a a relational database with the OS, then you wouldn't have had the right abstractions to make distributed databases like Dynamo and BigTable and whatnot. A database just has more design parameters than a file system and so you can't write one that will fit all applications. Again, the problem is underestimating the diversity of use cases.
So yeah I think both of these ideas are badly mistaken.
EDIT: I also don't think idea about shared memory is good idea. You can can have IPC without the network stack using Unix domain sockets, and that's what people actually use to connect to databases on the same machine. It has the benefit that you can move the database to another machine with minimal changes.
A shared memory interface between and application and a database sounds like a bad idea.