I removed the column that show the little enqueued and playing icons to free that little extra space. However, I find that I miss a way to identify enqueued songs, specially when enqueueing with the middle mouse button, that is kinda erratic.

I miss the visual feedback, but don't think I need an extra column to do that.

Is there a way to make, for example, enqueued songs italic (same way playing song is bold).

And the extra column could come in handy for people who need to know the order of the queue (meaning the icon could be changed to reflect this, with some kind of numeration going on... but this is better discussed in the suggestions session).

Though this is also a feature request, it's more of a "can I change the code quickly to do this?"

if you want you can use this column i made a while ago, it shows the track-number of a song or the playing icon or the enqueued icon (or modify the code for a column that meets your needs, which is possible btw):
{Column playandqueueandtrack}
menutitle = Playing/Queue Icon or Track
title = #
width = 20
sort = track
ico: icon(pad=2,icon=$playicon, hide= !$playing && !$queued)
text: text(markup=pesc($track.' '.$queued), hide= $playing || $queued)

How would I go about using your column?

you can add it to the other columns in /usr/share/gmusicbrowser/layouts (or whatever your $path to gmb is).

(i guess you can also put it in a separate file in ~/.config/gmusicbrowser/layouts/yourfile but i haven't tried it.)

It's possible to create columns that use italic when the song is queued. The only problem is that you need to create your own version of each of the columns you want to display. Or you can choose to only have the title become italic when the song is queued.

An example with a title column :
{Column title_italic_when_queued}
menutitle = title (italic when queued)
title = title
hreq=text:h
width=200
sort= title:i
text : text(markup='<span '.if($queued,'style="italic"').'>'.playmarkup(pesc($title)).'</span>',pad=2)