How do you estimate the chances of old legendary rework?

Just as title. How do you estimate the probability of old legendary reworks? I know that Riot team refreshes skins during VGU of champions, but for example Corki or Nunu right now are viable champs and their VGU will happen probably much later than sooner.

I guess it would be even profitable for Riot to rework them, cause so many mains or even casual players could buy or craft this skins. I like the release of new skins, but they could just rework the old ones, even one for patch would be cool. More login screens, more content.

Sry for probably bad english.