onMount async validation

[ruudandriessen]

We currently have async validators for both onChange and onBlur, however, none are available onMount. In our use case, we have a form where we pre-fill a name, however, we validate this is unique by sending an async request to the server.

We'd like to have this validated onMount, such that conflicts are shown immediately to the user - however, it seems we only have a sync onMount validation method. Is there any reason we don't have a onMountAsync?