Don't get me wrong, the bonus from Blademasters is great! But trying to build to get that bonus will make you lose every time. Fiora is extremely underpowered. Gangplank is very weak. The stronger Blademasters you don't get until late game and by that time you are lacking so much health one loss and you'll lose.
I've even tried to use other comps like Nobles early game and then selling to replace them with Blademasters, but that also leaves me at a disadvantage as some early game champions are very hard to get late game.
So you're basically left with trying to build a temporary team of Nobles (or whatever you want for early game) while also trying to build a team of blademasters on your bench which kills your economy.
The PBE shows a lot of changes to items and Demons, but nothing about Blademasters.... I really hope Riot does something about this!
TL;DR anyone who likes Blademasters is at a HUGE disadvantage.