Gharadelli Square hosts a chocolate festival every September but there is growth potential to do a much larger event. The annual chocolate festival in Perugia, Italy attracts almost a million people per year. Also, Gharadelli charges very high admission prices that most people can't afford and so there's a need for a free public festival.
Many big cities have an annual chocolate festival and they go far above and beyond showcasing exotic imports, vendor booths, and selling specialty products such as chocolate molds and thermometers. They have a lot of fun activities such as a chocolate sculpture contest, chef demonstrations and cooking classes, ice cream and beverage making classes, how to pair chocolate with red wine, showing a documentary about the history of chocolate making, exhibits of antique kitchen equipment, and other fun stuff that people expect to see at street fairs such as live bands, face painting. Art exhibits are always included but at a chocolate fair all of the paintings would have to be protected in plastic sleeves.
The weather would have to be cool so that the chocolate sculptures wouldn't melt. There are neighborhoods in San Francisco that stay cool most of the year, such as Ocean Beach west of the Outer Richmond district, but it's too far away from BART. The Daly City station is located in a cold micro-climate. There is a lot of open space out there but it's hidden; it's the Olympic Club golf course at 599 Skyline Blvd, the TPC Harding Park golf course at 99 Harding Road, and the Lake Merced golf course at 1 Harding Road.
A million guests would probably destroy the grass and so if the golf courses can't host the chocolate festival and it moves east than it would have to be held during the winter, probably in January because we already have the Cherry Blossom festival in February and the St. Patrick's Day parade in March.