Hi,
You can probably set receiver to lower motor speed to about 10% (might already be default) on fail-safe (frsky receiver manual)which guarantees some sort of smoother fall unless your pushing motors are up side down.
The code in next has extended GUI allowing to set failsafe on flight controller to percentages in addition to flight modes. I dont know anything about delayed failsafe isnt it delayed 1-2s anyway? Also to me safest failsafe is cut motors to 0% asap and I stick with that.
What would be the motivation of delayed failsafe, since delayed crash/landing of aircraft that has some error or isnt functioning sounds dangerous to me...