For starters, outlaw real estate speculation, at least the out of
control kind.

Impossible to define, and so impossible to outlaw, my lord, master of
high renown(fixed)

Real estate speculation won't last long without a lot of use of
someone else's money. How about banking regulations that say banks
can't lend more on a house than the minimum amount it sold for in
the past 5 years? (exceptions allowed if the property has changed
from a vacant lot to a house with land). If someone really thinks
the property is worth a lot and has a big down payment to risk it,
they can buy it at an inflated price at largely their own risk.
Wage slaves probably won't be able to afford a house with a rapidly
inflating price in the first place, so they wouldn't end up upside-down
on a huge mortgage and on the edge of bankruptcy. Perhaps the
prices wouldn't inflate so much if the suckers you want to sell to
can't afford such high prices.

The sales price history for a piece of property is public information
(at least according to local realtors and the local property appraisal
folks). The Federal government exerts a lot of control over what
mortgages can look like to be acceptable to government agencies
like Fannie MAE.

You don't have to outlaw private investment. If the private investors
go broke, it won't endanger the banking system.