Setting a specific pin to high status when the device powered

[pfeerick]

Use a comparator on the PMIC output pin for DCDC1;  with an open collector, and pullup for 3v3 or 5v.

Set the threshold on the comparator for something reasonable so that the 'off' level ( .3 , whatever ) snaps the output to zero and holds it there. The LM339 is good in this kind of application.  These make great level detectors, operate at a wide voltage range, and have open collector outputs;  pullups are 'required'.

Is there any particular reason a LM311 wouldn't be more suitable - as it results in a smaller package size, unless you want the extra comparators. However, that is beside the point - you're basically agreeing that unless the threshold trigger voltage for the linbus transceiver the OP is wanting to use will accept 0.3v as off if using the 3.3v power pins on the RPi/euler bus, that there is no reliable way to get a pin to go high and stay high immediately from power on, without using external hardware?