Other options is to trigger Pi on power state via amp on / aerial amplifier power which comes from bm53/54 tuner ( white wire ) I do this to bring up a auxiliary distribution power block which remote ons amps , dsp , and powered USB hub for my raspberry pi.I will do some tests but maybe you understand me wrong.
My pcb is designed to work with and without pi, but the powermanagemant i use with timer to cut off 12V after 7 minutes from relais which powers the ibus ic and all other consumers does not work (as the ibusbis not going down to 0V as i thought).
So i decided to use the pin 8 frim the ic which delivers 12V which i will use to drive a n channel mosfet which will then give ground to the relais. Waking up is done by ibus itself, no matter if pi is present or not, but how to shut it down via pin 2 if there is no pi present.
I'd need to find a way to send the 0V on pin 2 if there is no pi present. Thats the problem right now.
And also i need to send 3.3V to pin2 when the ibus ic is woken zp, if i understand the datasheet right?