And if you go on that direction, almost the everything on the language is a larger roadblock than an oddly placed conditional.
What do you think is more important: the speed at which C programmers can navigate your code base, or one person’s subjective idea of ”elegance”?
Specifically about Ruby, with it's infinite levels of metaprograming and "you can even redefine the meaning of blank space" philosophy, it's not 'unless' that will stop anybody.
That said, when reading code, I often have to pause and mentally translate "unless" to "if not". This is especially true for more complex logic.
Elegant, yes. Additional mental overhead at times, certainly.