A True Fan is defined as someone who will purchase anything and everything you produce. They will drive 200 miles to see you sing. They will buy the super deluxe re-issued hi-res box set of your stuff even though they have the low-res version. They have a Google Alert set for your name. They bookmark the eBay page where your out-of-print editions show up. They come to your openings. They have you sign their copies. They buy the t-shirt, and the mug, and the hat. They can't wait till you issue your next work. They are true fans...
Assume conservatively that your True Fans will each spend one day's wages per year in support of what you do. That "one-day-wage" is an average, because of course your truest fans will spend a lot more than that. Let's peg that per diem each True Fan spends at $100 per year. If you have 1,000 fans that sums up to $100,000 per year, which minus some modest expenses, is a living for most folks.
One thousand is a feasible number. You could count to 1,000. If you added one fan a day, it would take only three years. True Fanship is doable. Pleasing a True Fan is pleasurable, and invigorating. It rewards the artist to remain true, to focus on the unique aspects of their work, the qualities that True Fans appreciate.
Pretty much mandatory to link it with this: Nine Inch Nails makes at least $750,000 from CC release in two days.