It's a fascinating idea; of course, there are so many variants in existence of most of them that it would be an even more massive undertaking than it initially seems to produce any sort of "definitive" product, and, as noted above by GN, it's not even clear which were ever meant to be sung at all, and the extant tunes are often later additions to the text. But I love the idea---if, in theory, it were to be done, I'd vote for one of those huge, fabulous collaborative efforts---a real Who's Who in English folk/traditional music; it would be a REALLY exciting project!