Sure...why not? Terminal for iOS sounds like a good idea. Take some of this advanced functionality from the Mac and bake it into iOS. I don't buy the idea that mobile has to be what iOS currently is.
A replacement for HFS+ would be nice, however it's something that I hope that Apple takes awhile to work on. A new file system needs to be rock solid. It can't have bugs or flaws in it like iOS or like Apple Music/iCloud Music Library which scrambles metadata and deletes your music.
I'm definitely not joking. I used a terminal app pretty regularly on Android. Mind you, I was sporting a G1 which had the best physical keyboard I have ever used on a mobile device. With that said, I'm anything but a standard user.
Honestly, there are a bunch of mature options already. Linux supports a bunch of filesystems and has for some time. Some aren't rock solid but plenty are. I'd take ext4 over HFS+ any day of the week.
Given that they were talking about ZFS back in the Snow Leopard days, I'd hope they have something mature already. If there is one area where OS X is definitely backwards, it's the filesystem. HFS+ is really crappy. (Linus Torvalds has a pretty funny rant on the specifics.)
I don't understand the hype behind personal assistants on computers. They make some sense on mobile devices because you don't have a real keyboard or other good input method. But on a computer? I never use Cortana on Windows 10 (have turned it off, actually), and I doubt I will use Siri on OS X.
I doubt I would either. However, if it's any good my parents will be prime candidates. I find people who aren't very skilled with computers tend to be the most excited about this sort of thing.