First: if those initiatives are successful, they will not reduce or change the current RHNA housing allocation. They may affect future ones, but all cities are obligated under existing law to address their RHNA housing allocation.
Second: the viability of those initiatives appears low at this time. While there is enthusiasm among local elected leaders and some outspoken members of the public, the initiatives have not seen any financial backing that would help propel them to a ballot through signature gathering. There is no big interest group that appears ready to back the initiative efforts; without money, in a state like California, these are highly unlikely to advance.