I see what you mean by it being a stun with flavor, but I would think that him being forced to dance would stop the spin sadly there are no other champions with an ability that preforms a full particle animation of the champion. So the real question is, is judgment a channeled ability? And should sonas ult force him to dance?
Edit: You make a point with fiddles and Morg BUT both their abilities are non-cancelable while judgment is so those ults have a diffrent mechanic where they cant be stopped by any means where a player can stop judgment at will.