I've been thinking recently about runes, specifically keystones. There are a few keystones that are outright never really used, and if they are used, they are used by literally 1 champion out of 137.
Keystones like Guardian, with Nunu being reworked, Braum is now the only champion to take this rune over aftershock. So there's two things you could do with this, make aftershock a more jungle focused rune, and put more incentive/more reliable ways for tank supports to use it. OR reduce the cooldown so that mage supports can use it as a more defensive alternative to Aery, cause 70-40 seconds of cooldown for a shield and haste that lasts 1.5 secs is pretty shitty considering Aftershock gives 70-120 armor/MR for 2.5 secs with a flat 35 second cooldown (AND does damage) Perhaps you could even simultaneously make Ingenious hunter a more interesting rune and allow it to also reduce the cooldown of keystones? How interesting would it be to see a Janna or Lulu taking something like this https://prnt.sc/km0ikv Less league of damage, more league of variety?
Hail of blades is a rune that different champions have tried (Kindred, Xin) but the only champion who really takes it is Jhin, since the jungle meta favors Kindred or Xin to take Press the attack, since it focuses more on winning the early-mid, rather than the mid-late that Hail of blades favors (to help get their three hit attacks off faster for a quick execute)
The other rune is Glacial augment, again, a rune that several champions have experimented with (Swain, Sion) however the only champion to take it is Tahm Kench support, which is alright, it makes sense for Kench, but it needs more incentive for other champions to use it, other than the unique little trinkets that the rest of the inspiration tree provides.
I don't care if you disagree with my suggestions, I am just trying to get the boat moving, i'm more interested in everyone else's suggestions, because really these keystones aren't used at all. It's all Electrocute, Aery, Aftershock