This is a pretty mild set of reforms. An analysis of SB9 in particular, written by the Terner Center at UC Berkeley, is available here: https://ternercenter.berkeley.edu/research-and-policy/duplex...

Out of 7.5 million single family parcels, 6.1 million are SB9-eligible, and 521k would be market-feasible for construction. This would result in 714k new units of housing.

Clearly SB9 will moderately increase density in some neighborhoods, but it will only lead to construction on ~3% of all single-family plots statewide.