Not quite (though I hadn't realized, before this thread, that such an option existed); I was more thinking of tabbing in the opposite direction for minibuffer-complete.

I sort of lay out everything in the comment at https://midwest.social/comment/24082938 but the short of it is that I realized that minibuffer-complete does have functionality already built it: it just doesn't seem to work when trying to to autocompletion in Eval:. So I didn't realize that it'd work in circumstances like M-x.

Thanks so much for the suggestion, though! 'Appreciate the help.