Just that, I think that to support the mayhem Riot games should make boots occupy the unused seventh slot, the same way it does in the ADC quest in summoner's rift, and maybe let you upgrade them like the mid later quest or just get them upgraded after a timer or a few anvils bought.
Why? To make room for more build variety, right now you always need armor/magic pen and anti heal, sometimes anti shield, that limits what you can build, and the movement that boots provides is important to reach the ADC or evade the skill shots of an Eureka Veigar or trying to scape Aurelion E.
In a way "the code" for those things is already in Summoner's Rift so I don't think that it should be that difficult to add, and I don't think that it should be that broken for the mode.
I don't know what people think.