Ever take apart an engine that's been sitting for 6mo or 1yr? I have, and there's still oil on the bearings when taking the caps off. I am not sure where this notion of all oil disappears if the oil it left to "drain down". When air gets into the oil paths then there will be a lack of oil pressure during start-up time. Without pistons firing there is really nothing to worry about. One could put an inline switch to the ignition so that you can manually flip on the ignition after the engine cranks a few times to get some oil flowing. Or better yet, for engines where this "no oil" may be an issue, the OEM should program into the ECU a crank sensor count and will turn on the ignition after a few rotations of the crank.Back in the day old international Diesel engines were required to fill the filter with new oil before installing. I didnt do that on my Ford Diesel International with no problems. As long as you do the refill and start up soon, while the residual oil is still on the bearings. I always watch the oil pressure when starting to make sure that the pressure builds quick.