I had an idea for a cool mod.
This would work similar to the arrest related mods. You point you gun at someone, they put up their hands and then you cuff them, then they follow you around. Also like the current arrest mods, you can make them kneel or stand (important later). They will follow you into your car, even better if you have a van they will get into the back.
Once you have kidnapped someone, press a key to make a phone call (phone call animation) to demand your ransom (maybe kidnap someone from a rich part of town if you want to make any money from them). Then there may be an agreement made to pay the ransom, which will give you a waypoint to deliver the person to and collect the money. This can either result in a successful exchange or a police ambush. Or there is no agreement to pay, and you either get some Liam Neeson wannabe chasing you down using his particular set of skills, or they just can't/won't pay, in which case you have a body on your hands you can't make any money from and need to get rid of.
Hopefully you just made some nice cash, but if you haven't made the exchange, or maybe you've just escaped a police ambush, now is the time to get rid of your excess cargo.
Drive somewhere quiet and, maybe, release your prisoner.
More likely, put them on their knees and stay true to your word.
Having taken out your victim, you could then press a key to bury the body (if you are in the desert or countryside only), and maybe there is even a burying/digging animation somewhere in the game which could be used for this. The body effectively just dissapears while the buring animation/cutscene is playing. Perhaps you could even mark the grave with a placed item so you know where you buried peope.
That's my idea, what do you think?