I created pull request to main repository 6 days ago but as for now still hangs.

Sory, I forgot commit MySensors.h file, with definitions.
Definition "MY_PJON" sets transport to PJON.

/* Simple serial gateway with PJON transport and error handling */

// Enable and select radio type attached
//#define MY_RADIO_NRF24
//#define MY_RADIO_RFM69
#define MY_PJON //select PJON transport
#define PJON_PIN 12 //optional to change pin (12 is default)

#define MY_GATEWAY_SERIAL

#include <MySensor.h>  
void before() {
 //bus object is not initialized in this method
}

void setup() {
  bus.set_error(error_handler); //direct bus object access
}

void presentation() {
}

void loop() { 
}

void error_handler(uint8_t code, uint8_t data) {
  if(code == CONNECTION_LOST) {
    Serial.print("Connection with device ID ");
    Serial.print(data);
    Serial.println(" is lost.");
  }
  if(code == PACKETS_BUFFER_FULL) {
    Serial.print("Packet buffer is full, has now a length of ");
    Serial.println(data, DEC);
    Serial.println("Possible wrong bus configuration!");
    Serial.println("higher MAX_PACKETS in PJON.h if necessary.");
  }
  if(code == MEMORY_FULL) {
    Serial.println("Packet memory allocation failed. Memory is full.");
  }
  if(code == CONTENT_TOO_LONG) {
    Serial.print("Content is too long, length: ");
    Serial.println(data);
  }
  if(code == ID_ACQUISITION_FAIL) {
    Serial.print("Can't acquire a free id ");
    Serial.println(data);
  }
}

I created a pull request to PJON with change that allows define the broadcast address because in MySensors is 0xff.

I write new version based on development branch: https://github.com/4ib3r/Arduino
Unfortunately in this version new transport is integral part of library, but use of this is much easier.
Now I use synchronous send method with check acknowledge, and loop 500 times with random 100-600us sleep time for ACK, in tests this method is better than async.
Self PJON library is still required to run this transport and is not included.

@hek Indeed I forgot about the RS485, but PJON don't require additional elements.
Ok, I try to port this transport to development branch.

@Giovanni-Blu-Mitolo I know, but MySensors has several radio transports, but there is no on the wire.

Hi, I wrote simple transport for MySensors based on PJON protocol (single wire multimaster bus system). Actually this implementation is beta version but in my test enviroment on 3 nodes is working stable.
https://github.com/4ib3r/MyTransportPJON