There are currently a series of asynchronous methods in the RealmUser class, e.g.

public RealmAsyncTask logOutAsync(RealmApp.Callback<RealmUser> callback)

This method requires passing a callback object and process the result asynchronously. This isn't a problem per se. However, in case this operation is carried out within a reactive stream, users would have to create an observable themselves and deal with the emission themselves as well.

Having methods like

public Single<RealmUser> logOut()

would simplify things quite dramatically for API consumers.