Do those represent a "rapid accumulation of features" that create an "ever-increasing scope of the language" as the OP claims, or are they just tuning options? Keep in mind the Nim team didn't create the Boehm or Go garbage collectors, and the new arc/orc are the same, with orc having a cycle detector. If anything, it's a testament to the design and stability of the language that the GC algorithm is swappable.
Edit: for comparison, Java has four different GC algorithms to choose from[1] with a whole lot of options for tuning[2]:
[1] https://www.baeldung.com/jvm-garbage-collectors
[2] https://www.oracle.com/java/technologies/javase/vmoptions-js...
Many languages have pluggable GCs. Modern Java VMs have at least four (serial, parallel, CMS, G1). As long as they are interchangeable, it's not really a language design issue.
> I think you're stretching your narrative a bit. They're working on a new GC algorithm...
The thing is, according to the documentation [0], Nim already has six different garbage collectors.
[0] https://nim-lang.org/docs/gc.html