Edit: not my opinion, just what I found on the internets, not sure why the downvotes if it invites discussion.
As for the GP cited use case, there's no plausible way in which the compilers involved in the V8 build process would start using less memory due to their memory management machinery getting magically transformed by the hardware from tracing GC to refcounting GC, even assuming LLVM had been using tracing GC in the first place.
(Also the tracing GC memory overhead claims originating in Apple's marketing copy are way hyperbolic, modern tracing GCs don't require double storage used in "mark and sweep" GCs)
For normal users (such as people not compiling V8), swapping may be virtually unnoticeable.
For many people 16GB is absolutely enough, and Apple had to start somewhere. But if 16GB wasn't enough for you yesterday, it isn't enough for you now.
Those numbers are about 2-3x as fast as what my 2020 Intel-based MacBook Air gets.
But 2-3x won't change swap from grinding to a halt to perfectly smooth, either. It's still over 20x slower than RAM.
More significant for swap usage though is random reads and read latency, neither of which are going to be particularly impressive on the M1's SSDs. You need something like Optane to make that a compelling case.