"low income housing which is being demolished at unprecedented rates in Portland"

This is technically not correct.  Housing occupied by low-income tenants might be demolished to build luxury units, but without rent control that same older unit would still continue to go up in price past the point of affordability, given the staggering demand and low vacancy rate in Portland.

The only way to protect existing housing occupied by low-income residents is for community groups like Portland Habilitation Center, Hacienda Community Development Corp., etc., to buy them and add to their portfolio of designated low-income and/or for the construction of new housing that is strictly and legally designated as low-income.  That term doesn't apply in any legal sense to simply older houses where rents have been historically low for market reasons.