Currently if i set filter on my remote data source it fetches the data immediately, so if i want a callback i have to call fetch which will talk to server again.
What be really good is to be able to set sorting/filter and receive a callback when data is retrieved from server. 
E.g.
dataSource.fetch({
  filter: {},
  sorting: {}
}) // returns a promise
  .done(function(e){})
  .fail(function(e){});