The fallacy of that argument would be if its author would seek adoption, however like Naughty Dog with their Lisp based language, John has no plans to have Jai win world adoption beyone his game engine.
If Jai is happy to have limited adoption (which is fine), other languages will by definition not be displaced by Jai. That is even if we accept OPs implied point, that Jai is good enough to displace Zig, without further discussion. But even that seems to be rather doubtful.
That may be, but OP tried to claim that
> once Jai comes out, Zig will become obsolete
If Jai is happy to have limited adoption (which is fine), other languages will by definition not be displaced by Jai. That is even if we accept OPs implied point, that Jai is good enough to displace Zig, without further discussion. But even that seems to be rather doubtful.