As it says, it is something that is being developed or suggested but that is not yet complete and it is a regular expression in English speaking cultures, but in our case it is specially interesting for the case of James Joyce.

From Dr. Erin O'Connor paper, I quote:

Probably the most famous literary use of the phrase "work in progress" belongs to James Joyce, who made it the working title--or anti-title--of the book he began writing shortly after Ulysses was published in 1922. During the 20's and 30's, as Joyce began publishing snippets of his new project, he developed the habit of calling them fragments not of a work in progress, but of Work in Progress. "Tales Told of Shem and Shaun: Three fragments from work in progress," "Anna Livia Plurabelle: Fragment of Work in Progress," "Haveth Childers Everywhere: Fragment of Work in Progress," and so on. Joyce got the idea of calling his work Work in Progress from Ford Madox Ford, who in 1924 published the first bit of the new work in a special "Work in Progress" supplement to the transatlantic review. The phrase stuck, and remained the working title until the book was published in 1939--not because Joyce had not thought up a title, but because he did not want to reveal the title before he unveiled the book. His idea was that the title of the work should not precede the work itself, and that, moreover, his readers ought to be able to guess the title of his new book from the bits he had published during the seventeen years of its creation. (Joyce aided this experiment by dropping broad hints to his friends, who consistently disappointed him in their inability to surmise that the real title of Work in Progress was Finnegans Wake.)

Joyce envisioned his new work as a definitive statement: he said at different points that it would be a history of the world, that he was inventing an entirely new method of writing, and that it was to be the last word on language. The seemingly workaday phrase Work in Progress fitted perfectly with this project. In leaving out that all-important little article, "a," Joyce turned a process into a title, a work in progress into the Work in Progress. And in so doing, he demanded that his readers understand Work in Progress as an ongoing process of entitling: as the fragments added gradually up to a published whole, so the work would secure Joyce's status as the greatest of writers. All egomania aside, Joyce's refusal to supply a title up front makes perfect aesthetic sense if you've ever taken a look at the Wake. Nothing in Finnegans Wake is a given; nothing makes immediate or transparent sense. Such a work could not have a title that was simply given; such a work had to have a title that was, like the writing of it, and the reading of it, years in the making. As Joyce put it himself late in the Wake, "Work your progress!"

If we add the paragraph from Prof. James S.Atherton from his James Joyce Biography in the 1983 Encyclopaedia Britannica, we close the deal:

In Paris Joyce worked on Finnegan's Wake, the title of which was kept secret, the novel being known simply as "work in Progress" until published in its entirety in May 1939. In addition to his chronic eye troubles Joyce suffered great and prolonged anxiety over his daughter's mental health. What had seemed slight eccentricity grew into unmistakable and sometimes violent mental disorder that Joyce tried by every possible means to cure, but it became necessary to place her in a mental hospital near Paris. In 1931 he and Nora visited London, where they were married, his scruples having yielded to his daughter's complaints.

Meanwhile he wrote and rewrote sections of his new book; often a passage was revised more than 14 times before he was satisfied. Every word, every letter was scrutinized and pondered over. He usually began with a simple narrative. Basically the book is, in one sense, the story of a publican in Chapelizod, near Dublin, his wife, and their three children; but Mr. Humphrey Chimpden Earwicker, Mrs., Anna Livia Plurabelle, Shem, Saun and Isabel are every family of mankind, the archetypal family about whom all mankind is dreaming. The 18th century Italian Giambattista Vico provides the basic theory that history is cyclic; to demonstrate this the book begins with the end of a sentence left unfinished on the last page. Ideally it should be bound in a circle. It is thousands of dreams in one. Languages merge: Anna Livia has "vlossy-hair"- wlossy being Polish for "hair"; "a bad of wind" blows; bad being Turkish for "wind." Characters from literature and history appear and merge and disappear as "the intermisunderstanding minds of the anticollaborators" dream on. On another level, the protagonists are the city of Dublin and the River Liffey which flows enchantingly through the pages, "leaning with the sloothering slide of her, giddygaddy, grannyma, gossipaceous Anna Livia." An throughout the book James Joyce himself is present, joking, mocking his critics, defending his theories, remembering his father, enjoying himself.

Despite much scholarly study the book remains imperfectly understood; Joyce said he expected his readers to spend their lives on his book. It will remain a book for the minority, but it will always be loved by that minority. Since its publication it has had a great effect on many serious writers, as well as providing a new technique of word distortion and word creation for writers of advertisements.

After the fall of France in World War II (1940), Joyce took his family back to Zurich, where he died on January 13, 1941, still disappointed with the reception given to his last book. He would be pleased to know that, of the two periodicals now dealing with his work, one is entirely devoted to Finnegan's Wake.

This was back in the early eighties... Today, 2015, the "Work in Progress" not only about Finnegans but about Joyce can be figured out by the survey done by the James Joyce Society.

It is about time that someone, and I hope I did it, figured out some way to contain under reasonable and humanly average capability a format to cope with all that. Obviously we are dealing with a puzzle masterminded by a skillfull if not devilish man which is James Joyce. Essentially the novelty here is that instead of aiming at the puzzle, we aimed at its design and, instead of the regular bag of literature oriented tools, we used other sort of tools, specially those which made modern communications technology, such Internet, possible.

Computer based jobs are extremely suitable to recurring processes. It's sort of eternal return to the Entry Point which is the hallmark of this job and that's why the first (and the last) phrase of Finnegans Wake is up front.