You and I are on the same wavelength concerning the impracticality of siphoning from modern vehicles as well as infrequent dire emergency use and practicality of using direct car power for SHTF situation.Maybe a good thing for the idle to increase and let the ecu do what it thinks is best otherwise running out of fuel won't be what stops the vehicle!
I have 2 sets of jumper leads built-in ready for the apocalypse or when the car lights get left on.
Today's vehicles are different and I'm not sure what are the problems associated with long term idling, if any, since that's what city cars do most of the time anyway. In an emergency why not?
Glazing of cylinders was a problem in older vehicles, probably still is in diesel engines.
Make sure your vehicle is outside, carbon monoxide is insidious.
Siphoning from your tank can block the filters from plastic scraped of the hose after a number of times.
Most of the advice from others in this thread assumes that using the car's electrical system for my purpose would be a daily, weekly, or monthly operation when in fact it would be a rare, next to last resort action every few years at most - just prior to resorting to pure solar panel usage.