Yikes. Yes.

Not sure if other developers agree with me on this: I probably don't need autocompletion, I'm not writing an essay; I'm writing code where every character is a lot more impactful than forgetting a semicolon here or there. For this reason, having autocompletion could probably be an annoyance than helpful.

Personally I'm the exact opposite - weirdly for the same reasons you cited too. When programming I can usually predict what will come next or the compiler will usually slap me if I've done something dumb. Whereas it's easier to miss something in a shell because everything is a little more "golfed" and mistakes can go unnoticed for a while if you're being down-right careless.

I'd love it if there was a way to do a "test run" of a command line where it prints what it would do without actually touching the file system (for example).

Pretty sure a simple "dry run" is what you're looking for. Not sure what programs support it, but I know Docker for one does.

Sorry yes, "dry run".

There are definitely ways of doing it on a command by command basis but what I was more thinking about was a dry run on an entire pipeline. It's not a use case I tend to run into much these days though because there are usually better tools.