• An international reputation as a major musician spanning at least three decades;
• A decently talented ghostwriter.
In short, music memoirs are in, primarily because (quoting the article's anonymous New York City publishing executive), "they're pretty easy to produce, and with an already built-in audience, fairly cost-effective." That is to say: publishers are convinced people will buy a memoir by a musician, so they pour more money into the marketing and sale of the book, thereby creating the literary equivalent of a self-fulfilling prophecy. Well, sort of. Not quite. Partially.
Publishers are right that people will buy musicians' memoirs, which (à mon avis) is because they (musicians, not publishers) seem to suffer disproportionately from drug addiction, problems with alcohol, mental illness, hilarious/absurd/numerous sexual escapades, &c &c, and we Americans love us some sex and death in our entertainment. True, the publishers' commitment to higher advances and (in some cases) production values guarantees that they'll work harder (read: spend even more money) to move copies of the book through the register, but at the risk of repeating myself: publishers cannot create a bestseller without the reading public's cooperation.
While some musicians (and celebrities in general) are qualified to write their own memoirs, most aren't (and even those who are usually don't): instead, ghostwriters are hired to write their book for them. I'm actually not quite sure how the advance and royalty structure works for ghostwriters, but I imagine they're contractually entitled to a cut of the book's profits. Any agents and/or ghostwriters in the house: please feel free to enlighten me/us in the comments!
Now, to come full circle: if you don't have the aforementioned multi-platinum international rockstar of mystery career and qualified ghostwriter, all is not lost! You just have to get permission to write the authorized biography of some such celebrity. Which, I guess, might be difficult if you don't already have some sort of "in" and/or a proven publication record in journalism, memoir, creative nonfiction, &c.
Yes, well, while you ponder the implications of becoming a world-famous musician and/or journalist who covers world-famous musicians, I'm going to go pre-order Keith Richards' Life. To the Internet!