Apple is always experimenting with prototypes, so a report in today's Wall Street Journal doesn't necessarily mean we'll see these devices. But the details are fun to contemplate: they say Apple is testing an iPhone with a screen larger than 4 inches and an iPad with a screen that's nearly 13 inches. The article doesn't say what size iPhone screen Apple is considering, but an artist's rendering by Marco Arment on AppleInsider shows what a 5-inch iPhone might look like (second from right).
The Journal says that its info comes from Apple's suppliers. It's unlikely we'd see such devices until the latter part of next year. But this is more evidence that the market is moving toward offering touchscreen devices in multiple sizes. Samsung has been leading the way, with lots of options for consumers, including the 4.8-inch Galaxy S4 and the 5.5-inch Samsung Galaxy Note. The latter is sometimes referred to as a "phablet"—that is, a cross between a phone and a tablet. I've been impressed with these devices. And clearly Apple is considering moving in this direction.
To date, Apple has taken just the opposite approach: one size fits all. This has been a brilliant tactic for several reasons: 1) having a single model reduces manufacturing costs and increases profit margins; 2) having a uniform size is more appealing for developers, because they don't have to rewrite their apps for many different screen shapes and sizes (as with Android devices); and 3) market research shows that consumers have a greater tendency to purchase if there are fewer options.
In addition, Apple's philosophy has always been to keep its product line tightly focused in order to make sure each product was perfect. They're not interesting in making the most products or selling the most devices; rather, the goal is simply to make the best. And those who want the best will buy Apple, even if the price is higher. It's worked so far, as evidenced by Apple's $150 billion in cash reserves.
So why would Apple change now? It's hard to say. But my impression is that its approach to making products is to make many different prototypes to see which ones they like the best, which ones give the ultimate user experience, which ones users will love. As its recent video about their philosophy said, "There are a thousand nos for every yes." They don't a priori discount any possibility, but ultimately reject most prototypes.
The 13-inch iPad is the most intriguing. According to AppleInsider, Apple has been considering releasing a notebook computer that runs iOS. They suggest that a 13-inch iPad would fill the bill. It would have the sort of integrated case/keyboard that many manufacturers are already selling for the iPad. Essentially it'd be an extremely lightweight laptop with a touch screen and the familiar iOS interface.