You have a point, but I think there is a reasonable midpoint that Talos missed altogether. RISC-V's move towards RPi/Arduino style mini-systems lets them get a market going at a price point that has some chance to get some uptake early, and hopefully grow from there.
Talos seemed amazing, and I was always fond of the ppc/power architecture and wished for something more modern than an old G5 mac, but $7k for a desktop is just more than even most early adopters are willing to do.
That was the Apple Lisa's folly. It cost too much than most early adopters wanted to pay.
The PPC was a good brand but Intel out innovated them making faster x86 chips cheaper than PPC makers could. Apple had to move to Intel to compete with Intel PCs running Windows or Linux. Amiga still uses PPC but they are expensive.
Arm chips are so cheap to make that there is the $5 Raspberry PI Zero cheapest computer on a chip tech.
Risc-V would have to be priced like the Arm chips are, or else there would be no benefit to use them unless you like paying more for an open source chip that is free as in freedom and more expensive.
I am curious as a total novice why chips and why now? As you said ARM is cheap. For price to performance I don't see why there aren't multi-motherboards coming out.
Someone made a 10 raspberry pi MoBo which if it is cost effective would be easier than a cluster. I think it would be awesome if that was scaleable but I am sure there is a reason. It would be cool and save space making a cluster out of 4 of those boards rather than 40 rPis
Toy SoCs, like those used in almost every single-board computer, have bad I/O, which makes them poorly suited to general-purpose clustering. Also, general-purpose clustering is not something people strive to bother with. Especially not at a performance level that is as low as a bunch of Raspis.
Talos failed because Raptor tried to sell a high-end server in desktop clothing when the market called for maybe a PowerBook at most. They needed to start smaller with something lower-power.
The hole point of a free ISA is that many different people can produce them so that it will reach a economy of scale and chip producers will face competition making dirving down price.
With more producers, you get more competition, but LESS economy of scale, and for a product like this (with demand being limited initially), this was already a critical concern.
A point re manufacturing. Still, you get far more economy of scale than a proprietary niche product would have, plus excellent economy of scale re most chip design - where the real expenses are. Runs will be big enough to get most of the manufacturing benefits from scale.
I've pretty much given up hope on a non-x86 based chip hitting our desktops, the closest to reach will be ARM.
The economies of scale aren't there, I pretty much end up rolling my eyes at each of these articles.
[1] https://www.raptorengineering.com/TALOS/prerelease.php