I think that would be the primary motivating factor behind recommending Ellipsis, it’s already a builtin and we are not likely it to get another builtin singleton. Ever? But besides that “...” in a function signature, although maybe looking magical, does immediately call out to the reader that something special is happening  here. And for beginners who might not know that three dots are an Ellipsis or what an Ellipsis even is, it would be fairly easy to internet search “three dots in a function signature” or even “python def ...” would probably be enough to surface an explanation if this became somewhat common.