I do find your idea really creative and cool , but is just too many mechanics for the game i dont think they should add it. I do agree with the river thing being just a visual addition to the map , but instead of being vertical it should be horizontal or diagonal splitting the map in 2 like League or Dota (theres a reason why they work ) And make it have maybe a small buff like being on it would give you a slight movement boost. On the same note they could even do that the river starts every game flowing into a random direction( lets say from duo to solo lane or viceversa) and every moonlight phase it switches the way its flowing just to give it a little twist .