A list of methods riot could use to increase gameplay and decrease snowballing.

Make it possible to tp to any ally tower from the fountain.

Removing the walk to lane will reduce the amount of cs lost from backing or dying, and will increase the amount of time that you will be able to fight your lane opponent.

It will also inadvertantly increase the length of laning phase, increase the importance of individual towers, make defending outlier towers realistic, and will probably be an azir buff.

OR

Create a consumable that revives you at the fountain after you die. something like 50g, with a flag that causes it to no longer be purchasable.

Without death timers a walk back to lane will cause less cs loss, and will increase the amount of time in a game spent fighting an enemy vs watching the game through a grey screen. needs a shut off switch to keep games from never ending.

OR

Shrink the summoners rift map. with a smaller map more roaming and ganking become possible, it also decreases the walk back to lane.

Increasing every champions movement speed by a flat amount would achieve the same result.

OR

Make dying much harder. add a mechanic that prevents death unless a certain damage threshhold is hit. (like if you are at 1 health it can't go lower unless someone hits you for like 500) This will prevent weak players from falling to pieces or missing as much farm.

OR

Remove the 300 gold obtained on kill. players that die are already losing a lot of gold without the 300 gold.