Drats... looks like this feature already exists but is called "Column Guides".
Tools -> Tool Properties -> General Tab -> Appearance -> Editor Styles
-> In right pane, 'SQL Editor Column Guide' section
-> Show Guide at column [N]
Still, a possible enhancement. It would be nice to be able to have multiple column guides and to be able to set them to specific colors
I will open a ticket for adding more column guides.
Many different editors allow setting a vertical ruler (a line going up and down the editor at a given column count demarcation) for various purpose.
I use them in other editors to know when I've hit 80 columns and again at 132 columns to try and control my line lengths to stay within a printable page.
It would be nice to have them in SQL Commander editor tabs. It would require having a mono-spaced font but I'm that's a limitation I happily live with.