Once upon a time the tablet was being hailed as the device that would hammer the final nail into the traditional PC's coffin. However, five years since the launch of the initial iPad, a lack of innovation in the market is killing consumer demand for the device.

With Apple set to unveil its next iPhone handsets on September 9, there's also a very big chance that the event will also see the company unveil a new tablet. The iPad Pro, as it has been dubbed, is expected to sport four speakers, a 12-inch display and will be focused as much on productivity as multimedia consumption.

And it is being seen as the device that will breathe new life into the tablet market, which according to market intelligence company Trendforce, is in real danger of collapsing. It claims 163 million devices will ship in 2015 -- a 14.9% year-on-year decline. The firm puts this fall down to a lack of innovation and greater competition from 2-in-1 devices and larger smartphones. "Tablets have yet to evolve beyond their main role as entertainment devices," said company analyst Anita Wang. "And as smartphones grow in size, they pinch demand for mainstream tablet products that are sized at 7 inches."

The latest data from Strategy Analytics supports this shift in demand. In 2014, 66% of tablets shipped around the world had a screen size of between 6.9- and 7.9-inches but sales of devices with a 6.9-inch screen could have collapsed by 2019 as consumers move towards large screen (i.e., 10-, 11- and 12-inches) devices instead. Devices with an 11-inch or larger display will represent 7% of the global market by that time and 10-10.9-inch devices 18%.

An evolving format

The definition of the tablet is changing. The characteristics offered by early devices -- a bigger screen and the processing power to create and to consume -- are still in huge demand. However, it is now being met by bigger phones. The trend for phablets has become so big that even Apple introduced its first oversized handset, the iPhone 6 Plus in September 2014.

Also chipping away at the tablet is the Windows-powered hybrid or 2-in1 device which, after several false starts, is finally catching on with consumers.

"Just as phablets have eaten away at the smaller end of the tablet spectrum, the gulf between PCs and tablets is shrinking every day. Major vendors are pushing the boundaries of all three major mobile operating systems and hardware configurations to transform the tablet into a content creation device," said Strategy Analytics senior analyst Eric Smith.