These datacenters are already running old, inefficient, slow GPUs from five years ago in addition to newly released cards, because anything newer than that is extremely bottlenecked and they need all the compute they can get. Why should it be any different in five years' time? Even nVidia is rumored to be about to bring back the RTX 3060 which is an Ampere architecture card that got released around 2021. It's just fine.
Unless some disrutive technology comes along in 5 years time. And many are working on exactly that.
Yeah, conceptually this isn't all that different from new VM SKUs coming out in clouds. The costs and rate of change for AI hardware may be higher, and perhaps enough higher to mess up the math, but conceptually its a model that has been proven to work.