A customisable algorithm would be so good for this type of thing and honestly well suited to some sort of LLM powered interface.. I could describe my fitness goals in natural language and it could set alerts and metrics based on that, unstructured input mapped to a structured collection of settings..
This is the kind of thing I can see being useful, a tightly scoped set of outputs, rather than the "anything you want" nonsense the tech is primarily pitched as supporting