The due diligence you did yesterday is not worth much worth today. The one you are about to do will change tomorrow.
The people who move the market will be the same as before. The ones who can buy without mortgage. The rule was most likely made to avoid people overextending themselves in their greed for a fast flip.
The banks can either work to change this new rule, which may be difficult, or pass one the lost revenue on the their existing clients by increasing the interest rate.
It has always been an interesting volatile market and will continue to be so.