When I would make the Arduino boards, then I would make boards with a single ATSAMD21G processor and leave the AVR chips behind me. If a board with stronger outputs is needed, then I would still use the ATSAMD21G and add extra logic buffers.
The ATmega4809 can do everything a ATmega328P can do and more.
The main problem of a Arduino Uno is that the serial port is used to upload a sketch. The ATmega4809 has more serial ports, so also a serial communication to a Wifi module can be added without problem.
It is just a modern version of the Arduino Nano. That's all.
Okay, it needs a usb-serial chip to communicate with the computer. That can be any usb-serial chip. If that happens to be a more superior chip than the ATmega4809, so be it.
If you want a ATSAMD, then buy a Arduino MKR Zero. The ATmega4809 is a basic microcontroller for basic things. Without headers, the Nano Every costs 10 euros. That is reasonable for a basic board.