This assumes the client is oblivious to the fact that they are paying the same for 12 hours of work as they used to pay for 40 hours of work.

For non-technical clients that may well be the case for a while, but I suspect even the most non-technical clients will eventually realize they can claw back a good portion of the efficiency as discounts.

I'm negotiating some contracts where I could do the work in-house for about 1/20th of the previously-reasonable vendor cost. I'd rather not do it, so I'm happy to pay 1/20th plus a reasonable percentage above that, but that's the limit. The vendor can accept that, or goodbye.

Interesting times on vendor contract negotiations these days.