What are they going to name the tier below bronze, it's going to happen

Bronze 1 Bronze 2 Bronze 3 Bronze 4 Bronze 5 Dusty Rodgers

I've always had a soft spot for cardboard.

I'd go with Iron.

It's not offensive and doesn't make you feel like a scrub-lord, it's sturdy and malleable, a solid foundation for many things and shows a lot of promise to become something stronger, being the chief ingredient in Steel. Like Copper, Silver, and Gold it's also one of the 7 metals known of since antiquity, and it's a type of metal itself - so it fits in with the types-of-metals theme.

I half-hope Riot creates a Lead tier for all the weak players that are toxic and to heavy to carry though :P

On top there's Challenger and Master...

There's Diamond, there's Platinum...

There's Gold, there's Silver, there's Bronze.

And then there's you.

Garbage, sorry was that offensive? Technically nobody is in it yet, so nobody should feel bad yet :3

"Pyrite" aka Fool's Gold.

Alternatively, "Participation".

I've heard something like brass coming out as an idea

Wood PCV Tinfoil Cardbox

cardboard. definitely cardboard.

I almost feel like it should be some sort of "you aren't ready for ranked yet" thing. Perhaps remove their rank and make them win 3/5 promotional style to get back into Bronze 5.

I've always disliked that in normal competitions Bronze was an achievement, yet so many video games make it a catch all "here's your sticker" rank.