Battlerite, another topdown MOBA (much smaller) has recently released a battle royale where players go around picking up abilities and items. Why can't league do the same? The only thing in my mind is the map design because riot would have to make a completely new one and that would take a really long time.
The problem with bardle royale is that it is at most a forced team fight, there's no 1 v large number, theres no pick up good items, nothing. It's still fun, but it won't win the fight against fortnite.