If they think they can keep Dominion balanced by focusing on items instead of champions. There will be a subset of champions that are much better at this game mode than all others and they WILL be the only ones played unless Riot does something.
Proof? Look at 3v3. All you see is Singed, Tryn, Mundo, Jax and a few others over and over again. Unless they pull a Mundo and nerf some of the characters that dominate Dominion but are balanced on SR or even bad on SR like Mundo was then Dominion will be unfun as 3v3.
TL;DR; Some characters will be really good at Dominion and they will have to be changed unless they want Dominion to fail like 3v3 has. Even if they do people will rage because it will affect SR and cause still cause rage.