The main problem with slash as italics is that I very often write either file Unix file paths (like /etc/) or lists of alternatives (like vim/emacs/etc), and su

The main problem with slash as italics is that I very often write either file Unix file paths (like /etc/) or lists of alternatives (like vim/emacs/etc), and such markup languages tend to get confused. I rarely have that issue with * and _, since they only really appear as explicit symbols in code or math which already have other syntax markers.