I am going down the route of swapping in E46 Powered Sport Seats now and while waiting for my brackets from Lown Performance I figured I should get the Seat Memory work. All I had to go off was this YouTube video:
I was able to find an off the shelf LIN Bus Breakout board (same as K-Bus) and used an Arduino Pro Mini, figured out the wiring, and went as far as designing my own PCB to mount everything.
Full parts list and details / schematics here:
E46 Seat Memory K-Bus with Arduino and LIN-Bus breakout board
https://github.com/handro123/E46_Seat_Memory_K-Bus/
Demo:


I was able to find an off the shelf LIN Bus Breakout board (same as K-Bus) and used an Arduino Pro Mini, figured out the wiring, and went as far as designing my own PCB to mount everything.
Full parts list and details / schematics here:
E46 Seat Memory K-Bus with Arduino and LIN-Bus breakout board
https://github.com/handro123/E46_Seat_Memory_K-Bus/
Demo: