Only the 5 xmos chips costs more that 54$ in case you order only 5 of them 
but the Onju doesnât have that main component.
A little Confused, why are the xmos chips needed and could be go by without using them ?
Then I was also not sure if the Google Nest Mini Gen2 already finished its drop in replacement or what the current status on that is ?
@iMike78 I suggest that you also start a new dedicated thread here in the official Home Assistant community forum as well as in both the GitHub repos about your upcoming Crowd Supply campaign with a good title and introduction to clearify/explain that it for your drop-in replacment PCB for Google Home Mini (not Google Nest Mini) and that it will have almost the exact same feature-set as the Home Assistant Voice Preview Edition, including what the difference will be.
@LuxBoardGames FYI, iMike78 has posted under discussions in his repository on GitHub for his Google Home Mini drop-in replacement board that it is what he currently is focusing on first since the hardware design for that is already complete and that he is about to launch a pre-order campaign on Crowd Supply in just a few days in all goes well. Anyway, the PCB design for the Google Nest Mini (second-gen) board is not finished and iMike88 have put his work with that on pause until after the Crowd Supply campaign for the Google Home Mini (first-gen) board.
Yes it is needed in the use case, please read the original post in this thread as it explained in great detail there and it is explicitly the whole point with this thread.