I agree with the rest of the take but you seem to be coming from a developer's standpoint and I am talking about the user side. Developers back then also had access to terminal and knew how to use it. It's just that the entire software industry has grown.
When I was 10 years old, we had to write a turtle program in DOS. Tell me which 10 year olds today know CLI? They're all plastered to their iPads.
Prime example of juvenoia and biased stereotypical thinking right there. "Back in my days ..." ™
I know more kids in the ages up to 13 who are interested in actually exploring and working with technical stuff (programming and electronics for example) than kids who spend their most time just "consuming" and using these things. The main reason is that these things are much more accessible these days. YMMV, depending on your social and demographic environment I guess ...
Granted, I also set the bar relatively high. (Example: are those skills transferable.)
It does give me some hope that future generations will still use computers and not just tablets.
I'm not saying that's what you should do with Minecraft, but it could be interesting to see how such an interface is usable.
As I understand it, one would definitely need training/study to interface with it.
Though, to be fair, I started using a computer in the early 90s which was a DOS machine and only had the command line. So I grew up using a computer this way.
Making one-off tools to automate tasks, or even building a set of internal tools for handling certain operations is much more feasible when you can churn it out in an hour and be done with it.
Just today I spent an hour modifying an old cli tool to help process some customers that I could get as Csv. If I was to make a gui tool for this job, it might take a week or two and the result would be way less flexible.
If anything, CLIs are thriving on Macs and Linux boxes (in the cloud). Few people of my generation (70s/80s) would have ever predicted a whole new generation of hipster programmers and web designers today who think nothing of dropping to bash and ssh'ing and running npm. Or using vim and REPLs. We thought the whole world would go full GUI by the early late 90s (and it has, yet the console has continued to dominate).
Kids these days are more comfortable with the command-line than a whole generation of Windows programmers before them.
As for AS/400, I can't say I've interacted with it too much apart from a few brief occasions interfacing with DB2 on AS/400 and it was less than elegant (involved lots of emulation). We had a hard time building anything on top of it. The interoperability of AS/400 with non-IBM systems didn't seem to be that great, even though the system itself was rock-solid and ran mission-critical workloads extremely reliably.
I do miss the warm glow of a Turbo Vision IDE (I wrote my first real TUI application on Borland Paradox 4.0) and how quickly one could zip around and get stuff done.