At its initial launch the iPad was the fastest selling piece of technology of all time. It was usurped for that title by Microsoft's Xbox 360 Kinect. Interesting parallels between the two products, once deemed the future of computing and gaming respectively. The latter is being written out of history by Microsoft, almost certainly after the post Xbox One bundle launch which flopped hard.
The former though has a rather more intricate tale.
iPad numbers rocketed. From 7.3m in its first holiday season in 2011 sales all-but quadrupled to 26m in the same period three years later. That latter number marks peak iPad and since then Apple has been unable to halt a sales slide which now spans twelve consecutive quarters.
The sales numbers for Q1 2017 announced by Tim Cook are the lowest Q1 figures since that first holiday season on the market.
The iPad remains the best selling and most profitable tablet on the market and Apple continues to bank profits from the devices it sells. It's unlikely anyone at Apple is having sleepless nights even now.
It just looks like the hype suggesting a premium tablet could replace a laptop was overblown. Having owned one, most customers are finding there's either no use case or, in many instances, there's no use case at all.
Since peak iPad market either side of it has changed. Apple has embraced the phablet, Microsoft (and others) have delivered a variety of machines which fill the laptop and tablet roles in different ways and the iPad is left hanging in the middle being too much of one thing and not enough of another. It has reverted to being a companion device.
Once you agree the iPad is something you have as well as a PC, it no longer justifies a premium price. A cheap Android tablet with a good screen turns out to do that job just as well as the iPad. Alternatively an old iPad does just as good a job as a new one.
Rumours of new iPads in new sizes are common at the moment. Based on the limited success of the iPad Pro, I don't feel that the iterative upgrades being suggested will change the direction of the iPad market.
More likely new iPads will tend towards the premium end of the tablet price range and Apple will look to boost its average selling price by adding features (like the Pencil) which persuade fewer buyers to spend more money per device.
At some stage the fall in the iPad market will stop and sales will hit a plateau, if Apple is still making a healthy profit from the iPad at this point I doubt it will really care whether it sells one million or ten million.