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.