Earlier quoted context omitted.
Automotive EE here… I don’t think this is correct. If you are talking pre-electronic shift, your transmission still has position sensors and the engine or trans control module will not allow start while engaged. All vehicles have interlocks for this. Post electronic shift, it’s no question at all. You would need at least two errors in two completely separate circuits to get the vehicle to start in gear. Believe it or…
I may be misunderstanding what you're saying, but many modern cars I've driven will still allow themselves to be started in gear. It happened to me quite frequently until I built up the muscle memory for always starting with the clutch in, and occasionally still does if I forget (I drive a lot of hire cars).
But... If you are talking mtx (manual), which ones?
Because in 20 years of this industry I've never seen anything that didn't ship with a clutch interlock. So unless we're going back to pre-1997 - OR - you are in an "export market" like Asia, I am not aware of the models you're thinking of.