Yes, I know that's the basic plan for the next few years, but I am looking at this as a marketing activity over quite a many years and global geography.
Suppose Tesla starts selling cars in India. How many cars can they sell per year if they install only 20 Superchargers? How about 100 or 400? How might investors read the intentions of Tesla by knowing how much infrastructure (sales centers, service centers and superchargers) will roll out? So I am thinking that if you multiply the number of superchargers by 250 you should get a reasonable estimate of annual sales. So rolling out 100 in India would anticipate about 25,000 / year in sales.
For another example, suppose you live in an area with 5 Superchargers all within 20 miles of your home. That seems like pretty solide coverarge, and you should not hessitate to buy your first Tesla. But suppose your friends tell you that the wait time at those stations can be pretty bad sometimes. When you drive by one, you often note that it is crowded. So how inclined would you be to buy your first Tesla now? So I am arguing thay if Tesla wants to increase its sales rate in such an area it will have to add more Supercharger infrastructure in that area. If more bays can be added to a location, that will help, but more locations will generate more visability and may be needed for additional capacity. Visability is key to attracting new customers, and ample capacity is important to avoiding negative word of mouth from existing customers.
Another key feature of a 250 rule of thumb is that it supports pricing decisions. Basically when Tesla prices its cars it needs to allocate a certain portion of the selling price to the expansion and maintenance of Supercharger infrastructure. Say, $100k/year/station works out to $400 per car to be sold.