Current state of lore
The lore has been changing quite a bit, with champions getting new backgrounds and the lore being more fleshed out in general...
But what is the Summoner's rift in this day and age? Is the old Institute of War idea still canon? How nations participate to decide political and military outcomes through contests on the rift?
Since we are getting champions that clearly don't fit into this framework, I'm talking champions like Kindred or Illaoi or Rek'sai for example, I don't think anything in their lore suggests why they are here?