1) Training ML models does not require network access, which is one of the biggest competitive advantages of the cloud.
2) Training ML models is typically a batch process, which benefits minimally from the scale-on-demand model of the cloud.
Since the cloud premium is a significant exchange for the value that it adds, I don't see this being a big win for cloud providers. I can't help but think that if I were making use of extensive machine learning with continuous training, I'd have it training models on a local bare metal cluster statically scaled to my application's demand with minimal network connectivity needs. And then ship the serialized trained models to the cloud. The potential cost difference is huge.