That seems like a risky ploy. Guaranteeing that the existing AirBNBs get grandfathered in is far from certain. Then again, I've seen plenty of AirBNBs that just ignore the law so maybe it would be fine anyway. I once stayed in one that had explicit instructions on how to respond if someone asked you what you were doing at the house, which fake names to use and everything. Felt incredibly sketchy, but it was also about a third of the price of the cheapest hotel room in the area and didn't have cleaning fees or extensive checkout cleaning bullshit so that wasn't unexpected. Was a great location too.