Having the si5351 on the main board is particularly nice because it keeps the RF traces shorter.? The Arduino on the mother board makes less sense since everyone seems to be modifying that part of the radio as their first step. I like the whole concept though¡
That is a very nice layout. I'm torn though because I really like the ease of soldering SMD parts, it is much faster, however I like having the si5351 and Arduino onboard. This would make a nice uBitx with a Nextion display.