I don't think you can say that the project ever got as far as having a subject, but Dylan had a very beautiful idea.
I first heard of Dylan Thomas from Auden, in New York, in February or March of 1950. Coming late to an appointment one day Auden excused himself saying that he had been busy helping to extricate an English poet from some sort of difficulty.
Then in May 1953, Boston University proposed to commission me to write an opera with Dylan. I was in Boston at the time and Dylan who was in New York or New Haven came to see me... he was nervous, chain smoking the whole time, and he complained of severe gout pains...
His face and skin had the color and swelling of too much drinking. He was a shorter man than I expected, from his portraits, not more than five feet five or three, with a large protuberant behind and belly. His nose was a red bulb, and his eyes were glazed. He drank a glass of whisky with me and it seemed to put him at ease.
...As soon as I saw him I knew that the only thing to do was to love him...
Igor Stravinsky