Rogue's Riposte effect is displayed when the action is usable. When the Rogue parries shortly after casting Riposte, the effect is not displayed because the Riposte ability has a 6-second cooldown. However, it would be interesting to know that the rogue parried because s/he could prepare to cast the ability right at the exact moment the cooldown ends. Without this information, the Rogue may waste some disarm uptime at best, or waste an entire disarm at worst.

This would be an option. Usually, an effect like this is an invitation to suggest "please do something now". But this functionality means "please do something either now or in the near future".