[Billfred]

(Full disclosure, I work at a GM dealer and have driven more than my fair share of push-button start cars.)

The way I see it, the purpose of a car key (or fob) is to authenticate that the holder should be able to start it. If we can eliminate other related aspects that create undesirable conditions (say, having to keep the key where a heavy key fob can twist the ignition to off), it's worth a look.