Actually I have already several "not released" prototyping board. The first one (left of the above) is simple board with 3.3V LDO and 3-tact switch and MikroBus interface. The power is applied through "barrel" connector. The binary is uploaded through UPDI, indeed single wire, interface through Atmel ICE. At this stage, I noticed the importance of USB-UART interface and evolved to the next stage (mid of the above picture). It is pleasantly and comfortably working for checking and testing. But I am "OLED lover". Also the sample program on RTOS delivered by Microchip supports OLED display so the board has the evolution for checking it! (the right of the above picture).

The OLED is connected through SPI with ATmega4809 and as same as previous two version, still binary uploading needs the help of Atmel ICE. But I hope (may be not ?) Arduino.cc  will make bootloader supporting UART binary uploading and the DTR of CP2102 is connected to RST of ATmega4809 through 0.1uF capacitor, believing AVR traditional.

If you want to make board with ATmega4809, please use my Eagle library of ATmega4809. The file name of it is "microwavemont_ATMega4809.lbr" will be found in the above link.

It's no worth to imitate this but the circuit is like above. All of the pin has a pin-out or connected to certain devices. In the circuit you will see UPDI 6-pin interface. YES, it is really single pin connection, even without RESET....

Device recognition is as shown above. As a proof of AVR, it has Fuse bit!, but indeed ATmega4809 is more similar to ATXmega, not general AVR like Mega328 or Tiny series in the programming manner. (You will see if you touch this chip., like DDRB is not accepted by ATMega4809 but PORTB.DIRSET)..

Here is quick comparison between:

Actually I have no experience of Xmega, but enjoying ATmega4809 needs several knowledge of Xmega, not well-known simple AVR..