The keystone has some invisible power tied into it as well in its reducing summoner cd's. It wouldn't surprise me a bit if JG's/ tops start to use it in team play (access to double smite for objectives and then swapping out the smites for exhausts/ ignites/ tps) depending on whether the team is wanting to team fight/ split push.
Jg's with risky first clears can also make use of reduced smite cd particularly if they don't abuse another rune particularly well.
The more I use it, the more I like it. Also, the more it seems like it could become a big go-to Macro rune for pro play.
Just a thought- Top and jg could theoretically take this rune and smite at the beginning and actually trade off jungling and laning without giving up teleport or smite to do it which could work well if they deal different types of damage and the opposing top is itemizing resistances against one. Double smite the jg's first buff for them and swap it out for teleport if you're the top on your first back.