How can I trust that that push-button ignition will still shut off the car? I know it's conceivable that even a key-start ignition might turn all ignition control over to an ECM, but who's done that?
Saturn and GM did, somewhat. I have a 2006 Saturn ION and you turn the key to the start position and it "automatically" cranks the engine from there.
I hadn't completely shut my door one night and the dome light nearly drained the battery. I turned the key to start and let it go just like normal. The "computer" kept cranking the engine until the car started.