Typically, when you buy a home yourself, with mortgage insurance, you can basically go as low as a 5% down payment. If you're buying as an investor, you have to provide the 20% down payment, and therefore you can save on CMHC or private mortgage insurance fees, so there already is a gradient that's in there.
I think the reality here is that if folks have had these massive equity gains, they're not necessarily highly leveraged. They're bringing 30% to 40% to the table, because they can use their existing equity through home equity lines of credit and that kind of stuff. I'm not sure that such a mechanism would necessarily be effective, because they can go around it with these bags of money.