But Townshend took nearly 30 years to complete it: a longer conception than any other work in rock history. Now, it can be revealed, the piece, entitled Lifehouse, is to have its premiere.
A performance of an early version of the work was in fact given in 1971 to a small audience at the Young Vic Theatre in London, which I attended. Townshend had intended it to be the successor to his massively successful rock opera, Tommy.
But he then discarded the ambitious project which demanded `creative feedback' from the audience, and returned to conventional music making.
The completed project will surprise Who fans and non-fans alike. For it is clear now why it seemed so baffling in 1971. Townshend, in a particularly visionary phase, had foreseen the worldwide web.
The basic storyline, unchanged for the past 29 years, addresses the spiritual consequences of a move away from a physical, human community to digital networking and the power of music. At the heart of the drama is an 11-year-old, avisionary, full of daring ideas and dreams.
Perhaps reflecting Townshend's ascent to the arts establishment in the intervening period or rock's now classical status, its premiere in December will be on Radio 3.
Kate Rowland, head of BBC radio drama, said yesterday: "I feel sure that Lifehouse will be greeted as a contemporary classic. It's extraordinary when you think about what he was writing in 1971. It was like he was projecting ahead. He didn't use the words net or web. He called it `grid.' But he was hitting the nail almost right on the head."
Townshend, who has been adding to the original Lifehouse concept over the 29 years, has been working secretly with BBC drama executives on the project, and rehearsing a cast that includes Geraldine James, David Threlfall, Kelly Macdonald who appeared in Trainspotting, and 11-year-old primary school pupil Phillip Dowling.
Explaining the genesis of the piece in typically idiosyncratic analytical fashion, Townshend says: "At the end of the Sixties I was wary of growing tension between entertainment and commerce. My experience was salutary. Rock music was a bastard art form, and many in society tacitly approved the corruption of its exponents. Many Sixties rock artists and their cronies were Utopian visionaries, or bed-sit revolutionaries. However, their peaceful post-war middle-class upbringing instilled in them an innate belief in democracy, rather than direct action. My corollary ran thus: show business was corrupt and exploitative; the Establishment colluded.
"What made this bearable was the fact that rock had passed through its infancy and was occasionally generating spiritual uplift only matched in the classical arts. Technology and rock were hand in hand, marching to the future like a modern salvation army. Rock was a mirror to society, and reflected spiritual hunger.
"In the midst of all this uneasy anticipation, I wrote a play. If, in the future, life itself ever had to be experienced through art - let's say because of a necessary curfew to avoid the effects of radiation or pollution - a vast global network would be required.
"Would rock have a place or not? Was rock's particular brand of spiritual uplift - its main claim to be regarded as art - confined to live events before masses of people?"
Ms Rowland says that Lifehouse is more like a play with music than a rock opera. Townshend will sing the music himself, reworking most of the well-known Who numbers for the two-hour performance. The score includes several Who songs such as "Won't Get Fooled Again", "Baba O'Riley" and "Behind Blue Eyes", which were originally intended for Lifehouse. There will also be previously unheard songs by The Who's composer and lyricist.
For rock chroniclers, the completion of Lifehouse after its inordinately long gestation will be a major landmark, coming as it does from such a pivotal figure in contemporary music.
Townshend's most cherished project has taken on near mythic status over the decades and has been discussed by rock historians and Who biographers alike.
It is mentioned in the encyclopaedic Rough Guide To Rock, which describes the birth and apparent death of the project that it - like almost everyone else - thought had been abandoned. It notes how the music for Lifehouse set the tone for the coming decade. It says: "The band embarked [at the start of the Seventies] on a film/music project called Lifehouse which involved the band living with some of the fans, in the hope of creative feedback ... Retreating to the studio, The Who attempted to make something from the material they had got. Perversely, although Lifehouse was a major league failure, the resulting album Who's Next was probably their best. A remarkable collection of crunching riffs, power chords and anthemic lyrics - most notably `Won't get Fooled Again' - it virtually defined Seventies hard rock."
Townshend's 1969 rock opera Tommy, about a messianic deaf, dumb and blind boy, was eventually followed by another concept project in 1973, Quadrophenia, a hark back to the Mod era. But it is now clear that the project really intended to be Tommy's successor was, in its musical content and its prophetic storyline, a lost classic.