const contacts = createForm({email: string(), phone: string()});
const user = createForm({
 contacts,
 name: string(),
 location: { // i am inline form
   city: string(),
   country: string()
});

user.values.watch(console.log);
contacts.set("email", "blah"); // => {name: "", contacts: {email: "blah", phone: ""}, location: {city: "", country: ""}}
user.set("location", {city: "asd", country: "dsa"}); // => {name: "", contacts: {email: "blah", phone: ""}, location: {city: "asd", country: "dsa"}}

const ContactField = createField(contacts, ({value, onChange, error, validate}) => …)
const UserField = createField(user, ...)


const Email = () => <ContactField name="email" />

cold observables — это неверный ответ на неверный вопрос