College degrees are so necessary in modern society in large part because its discriminatory towards the poor to require them. In the same sense, investors want to be discriminatory towards the poor because they are not culturally like them. They want people of similar character, and since they can't be racist or sexist in whom they invest in without facing potential complications being classist by crowding out the poor is a viable way to "keep the riff raff" out of your money making schemes.
And it turns out making a city unlivable except for the top 5% of income earners is an effective way to keep the poor out.
I definitely think there's a strong classist component to who gets funded. Investors love pedigree. E.g., Zuckerberg not only went to Harvard, but he also went to a highly prestigious boarding high school, one that has a $1.25 billion endowment. Or look at Theranos's CEO, Holmes. She came from money and also went to an elite prep school (current tuition, $28.8k/year). For a time as a kid she lived next door to a famous venture capitalist in a town where the median income is $212k/year (and also 0.4% black.)
That said, I don't think VCs particularly care about what goes on in SF. Or anywhere. They don't need to make SF a citadel for the rich to filter who they invest in; they already do that well. But if it happens, I don't think they care except to the extent that it's raising costs for their portfolio companies. Even there, though, I don't expect them to do the obvious thing of getting on a plane and investing in companies in lower-cost areas. I think they'll just pressure their companies to open satellite offices elsewhere as a way of keeping labor costs (and labor power) down.
And it turns out making a city unlivable except for the top 5% of income earners is an effective way to keep the poor out.