ZFT
Personally, if I was king for a day I would have all level D sims freeze as the sim went outside the envelope for which the aircraft is cleared. Two reasons for this:
1 To get the attention of the crew in case they did not realise what they had done
2 To stop people using sims to establish what will happen to the aircraft outside the envelope when there is no guarantee that the sim is valid in such circumstances.
I sympathise with Cornish Jack’s need for off putting levels of vibration to be simulated. One US chopper sim I flew did this by shaking the seats rather than the whole cab. You can get very good fidelity like that with minimal mechanical engineering.