On one had - yes please, screw OSes, gimme something like Smalltalk environment (in it's Pharo incarnation preferably). On other hand - define OS. Isn't that Smalltalk environment an OS if it runs bare metal?
Yes, there is a very blurry line between operating systems, programming languages, and we can include databases as well. Some operating systems as you point out are PLs. Some PLs are implemented as databases. They’re all just really complex accounting systems by nature. Look at the implementation of a lot of OSes, PLs and DBs they are really just made up of tables keeping track of relationships all the way down.
None that immediately spring to my mind. There are operating systems that incorporate programming languages as their default user interface (like UNIX that drops into a Borne shell and LISP machines) and there are computers that have programming languages baked into their firmware (like the 70s and 80s micro computers did with BASIC). But in neither instance is the language itself the operating system.
The micro computer instance is definitely nuanced though. Some do argue that Microsoft BASIC et al were an operating system. Some don't. I'm in the latter category because I think "BIOS" more closely describes the function of the software on those old micro computers.