As many top smartphone and tablet makers struggle to grow their sales, it's hardly surprising that some big names are interested in bringing devices with foldable displays to market.

Eventually, the concept could take off in a big way. But it's best to keep near-term expectations in check.

An internal Microsoft (MSFT) - Get Report document picked up by The Verge provides fresh grist for the mill. The doc, which fits with some past reports and patent filings, describes a project (codenamed Andromeda) to create a pocketable Surface tablet with two displays that can turn into one large display when the device is folded open and one half is twisted around.

The Verge adds that the display "bridges the gap of the hinge when it's fully opened," and that engineering samples of the device look identical to concept drawings done by designer David Breyer. Microsoft is said to be "tentatively planning" for the Andromeda device to launch later this year, with similar hardware from other Windows OEMs launching afterwards.

Microsoft is hardly alone in working on hardware that pushes the limits of how much screen real estate can be placed on a pocket-friendly device. Others doing so include:

Samsung, which is working on a phone with a foldable OLED display. The device, referred to as the Galaxy X in some reports, is expected to launch by 2019. However, some reports have suggested that the device will have a four-figure price tag and ship in low volumes at first. OLED materials and patent-licensing firm Universal Display OLED ) - ) - Get Report

ZTE has launched the Axon M, a device with two 5.2-inch displays that appear side-by-side (with a hinge between them) when folded open.

Lenovo has demoed the Folio, a device with a flexible, 7.8-inch display that can be folded to function as a dual-screen smartphone.

Apple (AAPL) - Get Report , for its part, has filed a patent application for a device with a flexible display. True to form, the company hasn't announced any efforts to launch such a product. However, there have been multiple reports suggesting the company is at least exploring the idea of launching a foldable iPhone.

A lot of technical challenges will need to be addressed in order to make foldable mobile devices something more than a niche market. These challenges run the gamut from cost-effectively producing flexible display panels, to creating batteries and circuit boards that are flexible enough, to delivering adequate battery life, to making the hardware thin and light enough to appeal to mainstream consumers. To an extent, the harsh reviews meted out to the Axon M shine a light on how much work needs to be done.

As Microsoft's Andromeda project indicates, some of the aforementioned challenges are less daunting for a foldable tablet than a foldable phone, for the simple reason that consumers aren't accustomed to carrying tablets around in their pockets. Consumers might tolerate a foldable tablet being a little bulky when folded up, since they won't be carrying it in their pockets at all times. The story is different for a foldable phone.

Nonetheless, it's not hard to see why foldable phones and tablets could be huge over the long run. If we've learned anything since the launch of the original 3.5-inch iPhone in 2007, it's that smartphone users have had an insatiable desire for more screen space, provided the extra space doesn't make a phone too unwieldy.

Samsung's 2011 launch of its original 5.3-inch Galaxy Note was met with a lot of skepticism. Today, the original Note's display is actually smaller than that of your average high-end smartphone. A slew of reports indicate Apple plans to launch a 6.5-inch iPhone X successor this fall, to go with a 5.8-inch successor and a 6.1-inch, LCD-based iPhone.

With the iPhone X and various Android rivals sporting edge-to-edge displays that leave little room on the front of a phone for anything besides camera lenses and earpieces, foldable displays are the next logical step. And while it will take some time for smartphone and tablet makers to get the technology right, they have plenty of incentive to make doing so a priority.

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