This doesn't lower the value of the two story homes, it simply allows them to be bought out and developed. You say people are adamant to stay but I'm not sure that's true. You do see turn over, it's simply a limited supply.
Adding more studios won't crash the single family home market but will mean cheaper studios.
This is a self defeating sentiment. You're not going to drive homeowners out without buying them off. You're not going to serve more people with low density housing. Its just how it is.
With the availability of cheaper high density housing young people can at least start saving. There can still be nice high rise condos but the idea that everyone in LA and SF can have a single story home is just not going to happen.
Economic rents, unearned income, asset appreciation, constrained supply.