IIRC There is some discussion of using "-o", but then there are a whole slew of lexing/parsing issues that emerge since "o" is not part of the (vast!) class of characters Haskell considers as valid for use in operators. Regardless of that, I do kind of hope "-o" gets adopted...
Just -* and then pester the authors of Fira Code and Hasklig fonts (or fork) to add a ligation for the symbol when - and * appear next to each other =)