These highly-leveraged "new" companies and individuals make up only a portion of AirBnB-rented homes, which themselves are only a small portion of the entire housing market. There was a very recent interview or article with AirBnB's CEO where he (I'm sure he was fudging the numbers a bit) said only 1/3 of AirBNB homes are actually owned by these kinds of speculative home-buyers. The remaining 2/3 are split evenly between traditional real estate leasing companies and homeowners with only 1 house.
Also, worth considering that short-term rentals can easily be transformed back into long-term rentals. In any case, I think a national housing market plunge is highly unlikely.