For anyone still wondering about the way to bond together a "to" and a "from" datepicker - good news. It's achieved with help of getters and setters and here's how:
<div class="md-form">
  <input placeholder="Selected starting date" type="text" id="startingDate" class="form-control datepicker">
  <label for="startingDate">start</label>
  <input placeholder="Selected ending date" type="text" id="endingDate" class="form-control datepicker">
  <label for="endingDate">end</label>
</div>
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var from_input = $('#startingDate').pickadate(),
  from_picker = from_input.pickadate('picker')
var to_input = $('#endingDate').pickadate(),
  to_picker = to_input.pickadate('picker')
// Check if there’s a “from” or “to” date to start with and if so, set their appropriate properties.
if ( from_picker.get('value') ) {
  to_picker.set('min', from_picker.get('select'))
}
if ( to_picker.get('value') ) {
  from_picker.set('max', to_picker.get('select'))
}
// Apply event listeners in case of setting new "from" / "to" limits to have them update on the other end. If 'clear' button is pressed, reset the value.
from_picker.on('set', function(event) {
  if ( event.select ) {
   to_picker.set('min', from_picker.get('select'))
  }
  else if ( 'clear' in event ) {
   to_picker.set('min', false)
  }
})
to_picker.on('set', function(event) {
  if ( event.select ) {
   from_picker.set('max', to_picker.get('select'))
  }
  else if ( 'clear' in event ) {
   from_picker.set('max', false)
  }
})

Regards,
Kuba