That's the thing that gets me about a lot of posts (and this OP in particular). Here you have someone knowledgeable about the subject matter, but they've done little more than say "Harrumph! OSes used to be so much better! You kids don't know what you are missing!" and then not telling us what we are missing. Given that a large chunk of these OSes are consigned to the dustbin of history (either due to licensing, or lack of hardware to run them), it makes it harder to find out about them for ourselves. As the rule for writing goes, show, don't tell.

I'm not really saying the old OSes were better. In many ways we have come a long long way. Yes the command lines in the old OSes were better. They were easier to learn and understand. They had features that seem to be missing in many shells today. Things like autocomplete for example. But mainly I think we need more new stuff. Stuff I don't know is missing. I don't want a return to the old but a look to what would be new.

If you have to use a UNIX shell again, say bash, try looking into the bash_completions package (http://bash-completion.alioth.debian.org/). I hear tell that KSH and ZSH also do dynamic completions pretty well. Not sure if that's exactly what you mean, but I've found tab-completion to be getting better and better.

As for the great unknown, that sounds like basic research. Would love to see more of that stuff, but not many people seem to be paying for it. Still, much research is happening at universities around the world. If I hadn't given up on my postgraduate degree, that might be where I would be today :)