I think that at least for the 2nd and 3rd quartiles of the market, realtors don't add much value and will eventually no longer be part of most transactions.

Very high-end homes will probably always command a "concierge" style assisted sales approach. Both the buyers and sellers will want this, and be willing to pay for it. There is a lot more margin in these homes to cover the commissions.

Very low-end or badly damaged homes may require some specialized sales assistance as well, though most of those will end up as sheriffs' auctions anyway.

Before the internet, realtors were the gatekeepers of the MLS. You had to deal with them to find out what homes were available and what features they had. Now that is all a mouse-click away. So what value does the realtor add? Not much. They set up the MLS entry, and then wait for it to sell. The transaction itself is highly standardized. The lender and title company will take care of all all the paperwork, legally required forms, etc. What assistance an agent does provide (filling in a boilerplate "offer to purchase" contract, etc.) could easly be handled online in a LegalZoom fashion.

Realtors may help with peace-of-mind for the first-time buyer or seller. I used a realtor the first time I bought a home, and when I later sold that home. Reflecting, it was pretty quickly clear that they had done very little work for the thousands of dollars they took out of my pocket. I have bought and sold FSBOs since, and never regretted it.