IEO will be successful until the first disastrous project appears that will bring losses to investors, after this happens IEOs popularity will be equal to ICO. Exchanges today enjoy the "Skim strategy", due to the new idea of initializing tokens.
In the event of a project failure or deception of investors, this will greatly harm the exchange of which IEO was conducted. I think big exchanges are hardly to let it be. And they will carefully select projects before being placed on their platform.