The issue is, the tradeoff to making games shorter is that they become more snowbally. Let me try to explain, please stick with me.
There's a number of ways to make the game shorter, but in the end the objective is the same - kill the nexus. Assuming you want to keep the same map, shortening the lanes (and thus removing a tower) is out. Since the objectives can't be eliminated (3 turrets, inhib, nexus turrets, nexus), the only other way is to change game pacing.
You could condense the timescale - change the pacing of the game by making items cheaper, increasing gold, and decreasing objective defenses. Thus champions get items faster, deal more damage sooner, and push through objectives faster. This allows games to end faster, and is the basic direction Riot went.
However, if items cost less (or there's more gold flowing) and most champions are item-dependent, then a small lead leverages into a larger lead much easier - one kill/objective results in more value, allowing the killer to get items faster and putting his opponent further behind.
The same thing is true in teamfights - one team will have a gold advantage coming out of lane and will probably win the first teamfight. That can be leveraged into winning the next teamfight through additional items and objective control. Very rarely does the losing team have a chance to regain that lost ground.
If you don't mess with the map and don't mess with the items/gold, the only other direction to go is to increase damage across the board. In theory, if everyone does 50% more damage (but everything else stays the same) then teamfights are over faster without passing too large of a lead to the winning side. In reality, increasing damage does not benefit every champion equally, and could skew a fight in favor of one team comp over another. In addition, increasing damage results in more burst plays, where there is less time to react - which feels equally snowbally, especially when considering that objectives will fall much faster as well.
Overall, I can't think of a situation where games get shorter and don't feel snowbally.