I myself, several years ago, advocated for a completely new interface, because I was bored. But it didn't really happen beyond incremental changes, and I now think that's the best way to go about it--smooth out the rough edges with each iteration, bring the new when you actually have something new.I don’t understand the change for the sake of change, just to not be “boring”. I mean, I don’t get an iPhone for it to entertain me with a completely new UI every 2-4 years. I get it to use it, and I want it to work fast, snappy and efficiently.
Something that changed a lot throughout iOS 7, 8, 9, 10 and 11 was the Control Center, and I’m glad they didn’t change it again after iOS 11, because I find it useful as it is, and I’m used to it.