Earlier quoted context omitted.
The price will hit a ceiling at the exact time demand = supply, and not a moment before. A worldwide markets for these homes now exists, which means the number of people who both want and can afford them is huge, and therefore the price will rise until that condition is no longer true. Also, I believe we are again seeing signs of loan company shenanigans which, if so, will allow easy-to-game capital to continue to ch…
The "demand=supply" argument doesn't exactly explain why a foreign billionaire would want to own an appartment exactly in San Francisco. Personally, I would buy a flat in Ibiza, Barcelona or Hawaii way before even considering SF.
It's a self-perpetuating cycle¹: people invest in real estate; prices go up; it becomes a more attractive investment.
¹Sometimes known as a “bubble”