UIP is to much reduced for me.

I would better port something like the uc/ip or the KA9Q that coherent and DOS used.

Contiki and the UIP stack are very different from what we know of OS working.

The Mac OS is able to being hooked by experts in various ways.

TCP/IP on 16bit systems is no innovation,it only is a bit shrinked.

2.9BSD for the PDP11 got the TCP/IP stack from the VAX 4.1cBSD.