CNBC's Jim Cramer said Wednesday that Walmart could be the first traditional retailer to fully pivot to a fast-growing e-commerce business. “Walmart is no longer just a brick-and-mortar company,” Cramer said on “Squawk on the Street.” “We're going to start thinking of it as an e-commerce company.” Wall Street also sees a big opportunity for Walmart to generate serious ad revenue by featuring merchants' products on its Web site. Piper Sandler on Wednesday estimated that Walmart could quadruple its revenue from that stock over the next six years, from $3.5 billion to $14 billion. Piper Sandler has an overweight rating of “buy” on Walmart and a price target of $81 per share. The analysts said Walmart is “in the early stages of accelerating profit growth that is unprecedented for a large, mature retailer.” They cited the company's use of its e-commerce platform as a “new, high-margin revenue stream.” WMT YTD Mountain WMT YTD Stock Performance. Walmart's online marketplace is a fast-growing e-commerce platform that carries a wide range of brands from different merchants, and it's only been in the past few years that it's expanded in size. Piper analysts predict that the online platform will be “Walmart's biggest business driver over the next decade,” attracting more high-quality brands and creating a higher-margin revenue stream. Another key growth area for Walmart is fulfillment. The company said Wednesday it plans to open five automated distribution centers in the U.S. for its grocery business. This automation will allow the company to better forecast consumer demand and manage inventory. Costco, a retailer selected by CNBC Investing Club, is also focusing on online growth. But Cramer said Wednesday that Costco's e-commerce is not trending toward the same kind of growth as Walmart's efforts. Costco is scheduled to release monthly sales figures on Wednesday night, which could provide insight into its e-commerce activity. Costco management has stressed the need to invest in technology and alternative revenue streams, including digital advertising to monetize online traffic, as Walmart and Amazon have done. Costco's Year-to-Date Rise Costco's Year-to-Date Rise Costco and Walmart's stock prices have been soaring, ironically both up about 33% year-over-year. That's nearly double the S&P 500's gain of more than 17% year-to-date. Cramer cited both companies as the first retailers that could eventually join the trillion-dollar market cap club. Costco's stock market value is currently $391 billion, while Walmart's is at $562 billion.