[itsme]

my workaround using only existing features looks like this:
   
I use "dummy songs" as separators.

this works:
length = 0 prevents adding length
preceding dashes let them stand out in the setlist
the "next song indicator" announces the last song of a setlist
adding them to a separate collection "Separators" and a source type = separators allow filtering and separating them from 'real' songs

nice to have:
avoid increasing the number of songs in a setlist
different color in songlists (might also be useful to visualize e.g. swing / waltz / bossa or the like, so I'd recommend to implement it just as an addtional property of a song for maximum flexibility)

the provided examples look nice and useful