the market rate of return. You establish this by making sure that a market has enough participants that they all vie for the investment. This will drive down the rate of return, down to an acceptable level that allows participants to continue.
Also no amount of housing will fix the issue with people wanting to live all in the same place(i.e location, location, location). You can build your own house if you want to cut off the middle man but it won't be in the city center.
I mean I still prefer public housing but if we're on a mixed economy road, don't have a national pension model that works and people do market investment in property trusts for income class reliable returns...
The other suggestion is basically section 8 vouchers that the government already does.