The gating and/or shift stick pushbutton is regarded as sufficient safeguard against inadvertent shifting between a forward range and reverse. One cannot always save the operator from himself without compromising the utility of the machine.
It is worth noting that through 1965, the Chrysler automatic transmissions contained a reverse safety valve which, if the transmission were shifted into Reverse while travelling more than about 3mph forward, would place the trans into Neutral. It remained in Neutral until actually shifted into Neutral and then into a gear. This was a wise inclusion on the pushbutton-shifted Torqueflites, and was carried over through 1965 (lever-shift Torqueflites using the same twin-cable shift/park mechanism as had been used by the pushbutton shifters), but for '66 this feature was deleted along with the rear pump. No more push starts for Torqueflite-equipped vehicles, no more safeguard if you shift to reverse while moving forward.
DS