This just raises even more questions by users.
Does iTunes or iCloud backup stuff from the SD card? What if you restored on a smaller card cause you lost the old 128GB one and the new one is only 32gb?
When I download an app from the app store, how do I specify to download directly to the SD card? Does it pop up with a message every single time? How about transferring an app from iTunes to either the internal or SD card (because right now it's just a check mark, now users have to specify WHERE they want to download the app to)? And if I accidentally saved it to the SD card and want to move it over to the internal flash, how would I do that? In Settings app?
If the internal storage has 1GB free, SD card has 1GB free, that means I have to fiddle around and move apps to one side to download a 2GB app. Granted, if you just had internal storage, you'll just be forced to delete apps (which in Apple's eyes, is simpler than feeling the need to move apps around).
This app feels slow, and I don't remember if this app is on internal or external. How do I check? Settings?
There's a bunch of other scenarios and questions that I'm not even going to explore.
This is just a nightmare for obvious reasons. Users need to somehow transfer data through iTunes to a specified app or an common Movie folder so multiple movie apps have access to it. Developers need to decide whether to store data in the ubiquitous folder (iCloud), Documents folder (local), or SD card folder.
And you said "if one chooses options". How would you present this to the user? "Hey user, do you want core functionality on the SD card or just keep media files on the SD card". What does this even mean to the average user?!
This doesn't resonate with what Apple does. Apple doesn't add complexity so that a user can save money. They remove complexity and jack up the price. That's how it has always been. No more removable batteries in macbooks, no more internal removable hard drives in Mac Pros, no hard drive in Apple TV, and etc...
Lovely, but you and I know that if Apple wanted to implement an SD card everything you're throwing up as speculated complications would be worked through as "just works". Do I have to do anything special with a "fusion drive"? No, it takes care of what's in one form of storage vs what's in another form of storage in the background "invisible" to me.
Why would I want to go from 128GB SD down to something much smaller? That seems like it would almost always be the other way. But even still, what happens when I want to store something that needs more space than available on any Apple computing device? It tells me there's not enough room to do that and I am either given options or not.
I don't imagine people having to choose where apps will be stored, etc. Instead, they could make core memory in an iDevice work like the SSD portion of fusion: the stuff the system notices a person uses most is stored in core memory and stuff a person uses least is stored in the SD. If you then try to use something rarely used, it will do what Mac's do when you ask for a file stored offline: "Please insert..."
And so on. I get that you see fault with the idea and respect it in full. I wouldn't want the dreaded immense complications that comes with implementing an SD card slot forced upon someone so passionately against seeing the benefits of such an OPTION for those of us who would desire it.
My iMac and Macbook both come with such a slot and even in its use, I've never found it to be complicated, onerous, making either seem almost unusable, etc. Apparently, Apple can see utility in including SD slots in Macs. And apparently, it doesn't destroy the user experience because of the immense complications of usage someone like you can dream up. Perhaps I'm just to savvy to notice all the hoops you imply I have to jump through to leverage SD storage on Macs? My dear-old-Mom (about 69 years old now) has no problem using SD cards with her iMac either and I'm sure she doesn't consider herself technically savvy. Even little children can easily learn to off-load and on-load from storage cards. In fact, I can't think of anyone I know that has ever had so much problem as you imply using SD cards with computing equipment.
For myself, I find 64GB constraining and that's the biggest available iPad Mini. I like the mini just fine as is. While the next mini may have a feature or three that are desirable, I could easily see myself sticking with this one for several more years. If it had an SD slot, I could cheaply make it a 128GB mini right now. Next year or two, I might be able to make it a 256GB mini. If it could still do most of what I need then such that I wouldn't really need to replace it with a new one, I could just add storage... just like I do with Apple Macs. It's not mind-bogglingly complicated to add storage as needed to Macs. I'm sure Apple could work similar wonders to make it just as good a user experience to do the same with iDevices (if they wanted to do so).
And I bet you a bundle that if THEY chose to go that way, all this "how stupid that feature is" sentiment would flip very much the other way... even by some of the very same cheerleaders arguing against it right now (including, probably you). All that's needed to make the crowd here flip on a stance is for Apple to go a different way: an iSight camera was overwhelmingly stupid in an iPad until iPad 2 and then it was genius, a taller screen iPhone was stupid right up until it looked like Apple was going that way and then it was wonderful "shut up and take my money", and on and on.