The FT provides a brief history of the Bowie Bond. It seems the artist had a prescient view of the creative destruction the internet was going to have on music copyright and wanted to take some risk of the table.
”The absolute transformation of everything that we ever thought about music will take place within 10 years, and nothing is going to be able to stop it. I see absolutely no point in pretending that it’s not going to happen. I’m fully confident that copyright, for instance, will no longer exist in 10 years, and authorship and intellectual property is in for such a bashing.” “Music itself is going to become like running water or electricity,” he added. ”So it’s like, just take advantage of these last few years because none of this is ever going to happen again.
http://ftalphaville.ft.com/2016/01/11/2149761/a-short-history-of-the-bowie-bond/