Soft lock in AC is bumpy when hitting the rotation limit. We all know that, and even Stefano said in one of his streams that it's not working as intended.
I have a hypothesis regarding soft lock in AC and other games. Keep in mind that I only have a G25 to use and don't know if Fanatec/Thrustmaster/etc. behave differently.
I use a Logitech G25 with the Logitech Profiler software, latest version vom March 2016, having set a profile with 900° rotation as a persistent profile. One can set a persistent profile under Options -> Global Proifiler Settings -> Apply persistent profile. Whenever I play a game that features softlock (Like AMS or R3E) and after that switch over and play AC, the steering rotation of my G25 is out of sync with the on screen wheel (and steering for that effect), which moves faster than it should. Keep in mind that the steering settings in the AC options menu are still at 900°. The way to correct that is to switch the persistent profile in Logitech Profiler to another profile and then back again, so the standard 900° profile is again loaded as standard, or by adjusting the Degrees of rotation (DoR) manually in the Profiler software. After that, the on screen wheel is in sync with my physical wheel again.
What i conclude from that, is that
a) For example ISImotor games set the DoR by talking to the wheels driver software and setting the DoR there directly, as the settings carry over to other games.
b) AC does not communicate with the driver software when going on track, as it does not reset the wheel to the 900° as specified in the AC otions menu.
c) Other games seem to communicate, as switching between R3E and AMS sets either the automatic value for the car with soft lock enabled or the manually specified value with soft lock disabled.
d) Soft lock in AC seems to work by setting some kind of FFB effect as a bumpstop for DoR internally instead of in the profiler software.
//Edit: post expanded a bit