Unfortunately, I think you're right about not seeing this type of support. However, I think we see the implementation differently, because I don't think it has to be "contrary to the nature" of iOS.
You should be able to plug in an external drive and have access to it from apps that support those files. You already have apps that can open most types of files, such as File Browser. I can use that app to access files from my network shares almost like I'm on a computer.
I have a device called a Ravpower Filehub Plus. It allows me to access hard drives and flash drives, but the iPad has to connect to it via wifi. I should just be able to do the same thing by plugging in directly; it wouldn't really change anything fundamentally.
It would be very useful if I could keep things like office documents or creative assets (various forms of images, videos, fonts, mp3s etc.) on a drive and use them in a Final Cut or iMovie scenario, as well as be able to open office files from a flash drive, as well as download everything I mentioned from a browser. Ideally, you'd have a portion of your internal storage you could access for these things.
Having a file system in this way just means added functionality. It doesn't mean it needs to be like Windows or something, where you can launch executables and modify registry files. It just means you don't have to jump through crazy hoops like accessing files through File Browser, Filehub Plus to access your media, having tons of steps to copy files from your SD cards (which doesn't even work if the folder structure is off a little bit).
I think file system access, even in the limited way I've mentioned, is actually of primary importance looking forward, if this device is ever to actually replace a computer.
I highly doubt that we'll see that any time soon. Having a universally accessible file system is contrary to the fundamental design of iOS. If anything, we'll see Apple adjust the Files.app to inch things a bit further.