In scientific fields collaboration is the norm. There are distinct roles aside from the principal investigator, like, I suppose, the person who does the stats, everyone who performs the experiments physically.
In the humanities, the model is much more that you do your own work. There is no lab; there may be a working group. It is much more the model of the arts, where one person writes a symphony or a novel (typically). You don't imagine Proust writing a novel with a friend of his. There are collaborative poem, but they tend to be lighter in nature, and often fail even then.
I had an idea for an article / chapter when I was still lying in bed, before arising. "Lorca's Musical Theater." I could be my next Lorca lecture. The idea is to look at the music in the book Las canciones del teatro de Federico García Lorca and then branch out from there, with the thesis being that this music makes its way into films, other musical works, etc..., or is transformed /rewritten in various ways that have not emerged in the scholarship. This would be ideal for collaboration with musicologist.
I sent a trumpet fanfare from the book to my daughter to be recorded. She said it would be playable, though it is strangely notated. That might be a good addition when I'm giving a lecture. It is a "toque de trompeta floreada y comiquísima." [ornate and very comic]