Now the posix APIs feels like the worst of both worlds.
Most applications shouldn't really store data on the filesystem, and probably not even configuration. Most applications use a database for a zillion reasons (e.g. better backup, restore, consistency, replication, transactions, avoiding random writes, ...). Yet the filesystem is also not a great interface if you're building a database: you want more control over flushing and buffering and atomic file operations. The filesystem is mainly good at storing compiled code.
The "everything is a text file" interface is not great anymore, either. Simple manipulation of the output of basic commands (like text 'ps') requires error-prone parsing and quite some skill with things like grep, sed, awk, sort, etc. That's OK for experienced sysadmins working on individual machines, but doesn't integrate very well in larger systems where you have lots of automated access to that information. I have some experience doing sysadmin-like work, but I still run into problems with simple things like spaces in filenames and getting the quoting and escaping right in a regex. One option is for it to be more database-like, but that's not the only option. Erlang provides nice programmatic access to processes and other system information while still feeling very free and ad-hoc.
Of course, Linux is still great in many ways. But it feels like some of the core posix APIs and interfaces just aren't a great fit, and a lot of the interesting stuff is happening in non-posix APIs. And applications/services are being built on higher-level abstractions that aren't tied to single machines.
Is it time to look at database-first operating systems again? There have been a few. Tandem's Guardian was very well regarded in its day. Unfortunately, Tandem was acquired by DEC/Compaq, which tried to move it to the Alpha around 1997. Then, after HP acquired what was left of Compaq, HP tried to move it to Itanium. (There was a MIPS version in there somewhere.) After all those bad decisions, in 2014 it was finally ported to x86, by which time few cared. There's still an HP offering.[1]
In Guardian, the database system owned the raw disks. There were no "files". If you wanted something that looked like a file, it was just a blob in a database entry. Everything was transaction-oriented, like SQL. That was the whole point. Everything was a redundant, recoverable transaction.
The OS was cluster oriented. Adding or replacing servers was normally done without shutdown. Databases were replicated, and you could add new disks, wait for them to come into sync, and remove the old ones.
All this in the 1970s. They were way ahead of their time.