I don't think that's the plan op is talking about... the plan is if you change the housing rules so that the approval to build your apartment is state level rather than local level, then assuming it makes financial sense, developers can come in and buy single family homes on the open market and build something high density in their place.

There's a bill like this every few years, and it always gets shot down. The latest is SB827, which was shot down, too.

https://slate.com/business/2018/01/california-bill-sb827-res...

In general, the problem isn't with people being unwilling to sell to developers; the problem is that even after the developers get the property, they are prevented from developing it in a high density manner.