The target on this topic keeps moving as year succeeds year, but the tale told remains relatively consistent. Self-published authors are doing more and more books and making more and more money. The site Author Earnings tracks all this, (with a bit of rhetorical bias against traditional publishing, though that does not affect the validity of their data) and here I select a few snapshots from the last couple of years to show how things are going.

I don’t know whether this chart is encouraging or not. I guess we might take $50,000 as a sort of decent wage level, and this seems to show that there are almost 3,000 authors reaching that level on the basis of ebook sales alone in 2015. Not too shabby really. Also evident is the way the blue column overtakes the purple one as we focus more and more on recent data.
Author Earnings discuss the results of their research in considerable depth. As they say “The leftmost set of bars in every chart [their piece shows several charts covering different sales levels] includes all authors earning at or above a given level, regardless of their earliest publication date. The left-most purple bar is thus where we’ll find traditional publishing’s longest-tenured and highest-selling authors: names like James Patterson, Nora Roberts, Lee Child, David Baldacci, Janet Evanovich, John Grisham, and Stephen King.
The left-most blue bar is also worth a mention. Prior to 2009 indie authors were a niche phenomenon, with very limited access to mainstream readers. Six short years later, there are more than half as many indie authors earning steady midlist-or-better incomes from their Kindle ebook bestsellers as there are among ALL traditionally-published authors — even with all of those perennial traditional-publishing name-brand heavyweights, who spent decades atop the old-media best seller lists, also tipping the ebook scales.
So let’s take a look at the other sets of bars, moving across the charts from left to right, because that’s where things start to get really interesting.
When you look only at authors who started publishing less than a decade ago — in 2005 or later — the gap between the numbers of indie and traditionally published authors earning midlist-or-better incomes nearly disappears. Fast work, considering that none of those indies had widespread access to readers until 2010, giving their traditionally-published cohort-mates a five-year head start.
In fact, if we look at only authors who debuted in the “ebook era” — i.e. in 2010 or after — we see a reversal. At each annual earnings level, we find far more indies than traditionally-published authors who debuted in the last 5 years and are now earning that much or more.”
Here from a subsequent Author Earnings 2016 report is a similar chart showing the results at $10,000 for all formats of book.

Author Earnings’ Data Guy points out many authors enjoying significant sales in good-selling categories are not represented in this picture because the data they collect from Amazon is based only on the top 100 in any category*. The 101st book in romance say, may well sell more than most of the books in some other category. Recent moves by traditional publishers to increase the prices of their e-books must at least have led to a decline in unit sales (maybe $ sales also) though one might think its effect would be evident across all the columns. Firm information is this area is naturally rather hard to come by, though this of course doesn’t stop people speculating about trends. The temptation to regard any of this as saying anything about print should be resisted.
Jeff Bezos just revealed in his annual letter to shareholders for 2018 that over 1,000 Kindle Direct Publishing authors earned over $100,000 in royalties in 2017. Wow! How many of traditional publishing’s authors got that much? This chart from Author Earnings 2016 report suggests that it can’t be too many.

No question, self publishing is a category which is growing by leaps and bounds. There still remains a huge market for books from traditional publishers, and there remain thousands of active and aspiring authors who seek the validation of publication by a traditional publishing house. But will there come a tipping point when the volume remaining for the traditional publishing business is just too small to support their infrastructure? You can’t answer with a definitive “No”, but nevertheless you’d be hard pressed to say “Yes” and believe that that point was likely to come any time soon.
See Author earnings for some individual high earners.
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* And doesn’t include data from the old-fashioned bookstore channel plus other non-Amazon sales, which might alter the size of the gaps between them but probably wouldn’t change the relationship of indie/traditional publishing.