There aren't immediate plans to expand the pilot beyond San Francisco, but Instacart told TechCrunch that it's "considering" bringing the program to other regions, including other delivery services. This won't affect existing shoppers and delivery drivers.
Postmates sees this as a logical extension of a recent strategy that includes expanding Walmart's grocery deliveries. While this won't overshadow its core delivery business, it hopes to fill in the gaps for other companies that can't always hire more couriers. In other words, you could eventually see Postmates at your door on behalf of many companies, not just a handful of partners.