So will developers have to redesign their apps to bring the visual look more in line with this new version of iOS? The old iOS had such a defined design languag

So will developers have to redesign their apps to bring the visual look more in line with this new version of iOS? The old iOS had such a defined design language, I wonder if opening an app that doesn't have the new "flat" look will feel terribly inconsistent or jarring. The free radio service sounds unbelievable though. I'm very jealous of iOS users just for that (even though I'm not a big music listener)