Well, providing the replacement engine as part of the language compiler package as a simple command-line tool you can hook into your editor of choice as a hotkey so I can say "replace all the operators in this file with their appropriate mathematical unicode counterpart".

This is what e.g. many Haskell developers do, the issue is that this will usually fuck up alignment (because the base font does not contain the non-ascii symbols) and generate different alignments between different viewing contexts. It also leads to odd issues where deleting a character just changes it and doesn't move the cursor at all.

Ligatures are a time-honored way to improve the look and feel of combinations of characters, that's basically the entire point of them.