Thanks for the update.
One thought I have is whether this type of approach with radio driven by a software driver can even work reliably.
Latency is of utmost importance especially when ACKs are involved, and a low power node cannot sit in RX mode a "long" time to wait until a OS decides to give attention to a received package at the gateway, and then wait until it has the next turn to the GPIO to send a reply.
I have not even tried actually, hence my blurb. I have always used a Moteino which handles all the RF part, or lately the
RFGateway board. Then the Pi has no knowledge of the RF part, and can nicely meet the separation of concerns pattern.