Skeuomorphism existed for decades before it was fased out with ios 7, flat ui is still relatively new compared to that and we're unlikely to see an other dramatic change in design anytime soon.
But for now I'd be happy of flat design got a but more physicality like shadows and depth and effects...so not very flat....and if ios 18 gets the same language design as visionOS than that would be a big step in the right direction.
It seems to me like visionOS is thier new design language which we'll start to see more of on other platforms, tvOS already got updated with some parts that look straight out of visionOS.