It’s on my list for Easytransfer 2.0 with advanced options. Though because of my upcoming wedding I don’t have a time table for when that will be done.
In the mean time if you need an ack scheme it wouldn’t be too hard to implement.
if(ET.receiveData()) Serial.print(“A”); and on the transmitting end have it send data, wait a bit then look for an A coming back. If no A comes back send again.