I used to think so, but in industries where supply is abundant, publishers provide not only "post-production", but distribution and more importantly marketing and branding - social proof. The biggest benefit may be setting oneself apart from the fray.
If publishers die, such social proof will simply come from other venues, be it dedicated marketing outfits or some sort of community (goodreads etc). In music, major labels are increasingly irrelevant.
And then successful dedicated marketing outfits starts vertically integrate to beat out competition, offering editorial services, distribution, etc.... becoming a publisher.
What will happen is that some publishers fail to adapt to a digital economy and are replaced by upcomers who are perfectly adjusted to it. Publishing companies will not disappear because they fill a function in the industry.
A "publisher" in the digital world will be a very different beast and it will be hard to call it such. Most of it will likely be automated. Their core-competency might not even be book-publishing.
Are Amazon and Netflix "studios"? No, but they do produce high-quality video content. Is Louis CK a "studio"? No, but he's producing a TV series.
Publishers' functions (content editing, packaging, distribution, marketing and merchandising) are being split and reorganized in different ways. Verticals built on the new production chain will look very different from current publishers.
They pretty much are in today's sense of "studio." The days of MGM having a bunch of actors under contract and cranking out movies on their backlots and sound stages is pretty much ancient history. Studios are mostly the moneymen for independent production companies--which is the case whether the studio's name is Fox or Netflix.
Recommendation engines are real and are improving. Spellcheck fixes typos and some decent neural-network training can be pushed into literary land (already MS Word "dares" here and there, and that's not even centralized). Would a "digital editor" be foolproof, or particularly good? No, but it would likely do a lot of the grunt work fairly reliably, so you can shrink the workforce or increase output (more books, argh). When I hear of the "slush pile", I cringe. That's a job for a machine and not a very smart one at that.
> Netflix and Amazon are studios
No, they are content distributors who happen to produce content because of supply failures up the chain. The middlemen upstream are failing to see opportunities, so downstream is taking charge. The minute this changes, they will go back to being content distributors because that's what they do.
Source: I'm a smalltime author and publisher.