@Riot or smart people, with the new Ancient Coin Passive, does the 8% movement speed...

My Janna main club comrades inform me that movement speed boosts are typically additive, resulting in a 16% boost.

It's noteworthy that there are diminishing returns on movement speed though, so a 16% movespeed boost does not necessarily result in moving 16% faster. Theres a breakpoint at 415 movespeed, and another at 490 for those who build up loads of MS.