Two years ago I published this: 2015: The One-Terabyte iPad.
I roadmapped what I thought the increase in iPad storage capacity would be:
2010: 64GB
2011: 128GB
2012: 256GB
2013: 512GB
2014: 750GB
2015: 1TB
Today: Apple ready to release additional iPad model; likely 128GB version
Really, I feel a bit insulted that Apple is only now going to release a 128GB iPad, which will likely cost a $100 premium over their 64GB model — that’s how Apple’s pricing works.
You know, it could well be that another factor that accounts for the rise of Android (see here and here) is that people can add more storage on their own.
Apple, it’s time to add a damn microSD card slot to your devices.

Moore’s law doesn’t happen every year. It happens every 2 years. Apple didn’t double the storage of the first iPhone in the 2nd iPhone. They did it in the 3rd one.
But they have been lagging in this though.This report of 128 GB doesn’t even make it sound like they will just double the 64 GB version, and presumably also make the 32 GB version the default one. It just sounds like they will add a 128 GB option. That doesn’t sound good at all.
Another point to consider, though, is that Retina eats up a lot of storage space for the higher-res graphics. And if you want to view pictures now, you want the larger files of those too. HD video is also massive. I’m surprised they actually offer a 16GB for Retina. It should begin at 32GB. And if they added a microSD slot, people could add whatever additional capacity they wanted.
I agree with you that the upgrade harmony gets disrupted, but Apple is trying to balance many things, including space, battery life, heat, weight, speed and of course price.
Frankly Apple has hundreds of billions of cash so I would be inclined to think they know what they are doing most of the time. For every maps screwup, they make thousands and thousands of very good decisions.
The same could be said of any company once in its prime that is now gone: Digital Equipment, Wang, Palm, etc. It’s not always obvious what the knife blade is that leads to a fatal cut.
It’s idealism vs. realism. Doesn’t matter how much Apple pays for it, SSD is still a finite resource. One 128GB iPad consumes as much SSD capacity as eight 16GB iPads. It may not have been strategically sound to devote that capacity to 128GB iPads early on (especially with the new Macs consuming a lot more SSD too).
It is also possible that a 128GB iPad is a cynical attempt by Apple to maintain their lock on global SSD supply during the post-holiday sales slump, allowing them to maintain their SSD buy-up rate despite selling fewer iPads.