Sounds like you have essentially replicated the functionality of this service (TrackPIN):
Indeed, we discussed the pros and cons, and whether or not emulation via SmartThings was feasible.
Personally, I am looking for outdoor compatible smart locks for both our entryway gate and our backyard gate. The backyard gate is not an emergency exit, and so would ideally have a keypad on both sides, or perhaps we would use SmartThings unlock for exit purposes.
The front gate is where our delivery persons leave packages now, as they are aware the gate is not kept locked. Luckily we have not had any thefts, and we will probably add a camera there to help reduce the risk.
The concern I have with your setup is convincing the vast variety of delivery services (Amazon now has contractors do deliveries on Sundays, etc., Google Express, etc.) to follow the procedure.
TrackPIN, linked above, has apparently established contracts and procedures with specific delivery companies.