The Formula Tool does a good job of autocompleting expressions (for example an open square bracket will show you variables in your dataset), as well as syntax highlighting (coloring variables, keywords, strings, etc).
I propose having this feature available in all tools that use the expression editor, particularly common ones such as the Multi-Row Formula Tool and the Multi-Field Formula Tool.
This parity across tools would provide a more consistent experience for the user and increase one's productivity using these tools. It's incredibly helpful for beginners and seasoned Alteryx users alike and should be available wherever possible.