Over the past few years, the trend has been for smartphone screens to get larger and larger. Back in 2010, even a 3.7-inch model could be a top-tier handset, but nowadays we expect more like a 4.3 or even 4.7-inch screen. There are some signs that we're not even done yet, and five inches could become the new normal; just look at rumored devices like HTC's 1080p five-incher or the Galaxy Note 2. This is hardly restricted to Android, and after years of the iPhone sticking with a 3.5-inch screen, Apple finally looks like it's moving on up to a four-inch display. Why, then, isn't the same sort of thing happening for tablets? For the most part, the industry seems comfortable topping-out at around ten inches, as it has for the past couple years. Will we ever see something like a 15-inch tablet?

Why would you want a 15-inch tablet? Personally, I can't imagine life without a general-purpose computer, but a growing number of users are dropping their laptops for tablets. So long as your computing needs can be addressed by what apps are available for the platform you choose, it's not an entirely unreasonable proposition. But once we start talking about living your entire digital life on such a device, even a ten-inch screen can start sounding cramped. Especially if you're going to be doing business on a tablet, working with large spreadsheets or proofing layouts, having some extra screen real estate to work with sounds like a godsend.

So far, manufacturers have only started to scratch the surface of jumbo-sized tablets. Toshiba's got its AT330, a 13.3-inch giant (above). We've also seen evidence emerge from the Apple v. Samsung legal proceedings that suggests Samsung's been working on an 11.8-inch model of its own. That's a step in the right direction, but if manufacturers want to see these 10-inch-plus models find success, they need to pay their designs some special attention.

Not like this.

Take the Toshiba, for instance. It may have a huge screen, but that display only has a 1600 x 900 resolution. That works out to a pixel density of just 120ppi. Contrast that with the 10.1-inch Acer Iconia Tab A700, which achieves 224ppi with its 1920 x 1200 display. If the primary purpose of large tablets will be to replace laptops, they need to have the components to match. A 1600 x 900 resolution for a laptop screen that size isn't really that bad at all, but when that market's stepping up to the kind of resolutions like the latest MacBook Pro supports, tablet makers will have to keep up.

We'll also need to see manufacturers pay special attention to usability. Above the 10-inch mark, holding a tablet while you use it becomes increasingly unwieldy. When you want to enter text via on-screen keyboard, that's even more true. How might that be addressed?

I think Samsung has a good thing going with its S-pen stylus. A generic capacitive stylus just doesn't have the precision a good pointing device needs, so Samsung incorporates a Wacom digitizer in its Note series of devices. We've yet to get a chance to try out the Note 10.1, but I've got a feeling that it's going to absolutely shine with the S-pen; in the same vein, stylus input could become very important with even larger tablets.

Even if users are ditching their laptops, there's a lot to be said for holding on to a hardware keyboard, whether that's built into a case like Microsoft's innovative Surface design, or just a separate Bluetooth model. In either situation, tablet manufacturers would be wise to follow another page from Microsoft's playbook and offer built-in stands. At 15 inches, you're going to want a convenient way to prop that big screen up at a moment's notice.

Though this kind of size presents new problems, it's also rife with opportunity. We could see tablets arrive with full-sized ports, ready to take advantage of all our PC accessories. Think: full-sized USB, no more adapters for HDMI, and support for standard SD cards. Heck, we might even see tablets that switch from hard-wired storage to supporting solid-state laptop drives.

Obviously, as we talk about larger and more feature-rich tablets, we're also looking at a similarly growing price tag. That represents a problem, because as we cross the $800-or-so barrier that marks the top of the price range we expect from current tablets, it becomes more difficult to justify such a purchase in the face of more capable laptops. For some users, the tablet form factor will easily justify the expense. For the rest of us, manufacturers might find themselves having to pay even more attention to keeping costs down than they do with smaller tablets.

Will a 15-inch tablet find a home in your stable of devices if such a thing ever comes out?