[0] https://www.supremecourt.gov/opinions/20pdf/18-956_d18f.pdf
[1] https://en.wikipedia.org/wiki/Google_LLC_v._Oracle_America,_....
Edit: Changed phrasing of question. Also, to be clear I think the answer is probably yes.
In contrast, reimplementing a copyrighted ISA would quite clearly be substantial and could easily have large market effects. So you'd have to lean heavily into the idea of interoperability to overwhelm the lack of these other factors, or argue that the ISA is not copyrightable per se.
Also, even if an ISA isn't copyrightable, you have to watch out for patent rights the owner might have over any part of the ISA.
The vast majority of ARM licensees aren't doing anything transformative, that's for sure. But would something like the M1 - bringing ARM to the desktop when all past attempts have failed - have been considered transformative?
The question of what constitutes a "large market effect" is a big one...if I make a chip to serve as a controller in my brand of hard drives, is that a large market effect? ARM loses out on a few pennies per drive or something.
And I'd dispute the characterization of micro-architecture design as "insubstantial". Not accusing you of this, but this really has been the most frustrating thing about RISC-V - software engineers who don't know anything about CPU design comparing it to Linux when really it's more like POSIX or, yes, the Java class library. The insides of microcomputer CPUs haven't really resembled their interfaces very much since the early 80s - even the 68000, a consumer-grade CPU that's 45 years old (!) was designed so that the microcode engine that drove it could be used to implement an array of instruction sets. Any useful implementation of a CPU has an enormous number of internal details that aren't implied by the ISA.
If anything, I'd say that it's precisely because of this independence that an ISA can be seen as a separate work from any of its existing implementations. So what I'm trying to get at, is that if an ISA is copyrightable at all, in whole or in part, then any complete re-implementation will be copying most of the ISA's own substance, regardless of differing internal details. (Where by 'ISA' I specifically mean the external interface that software can access.)
What restricts new implementations are:
1. Existing legal agreements, eg if you agree in a contract that you will treat an instruction set as protectable IP, you’d be violating the contract. (Assuming the contract is valid.)
2. Patents, if you need to violate a patent to implement an instruction set then you need to license or wait out the patent, or figure out a way to work around it.
I believe both of these were at issue in Intel v. AMD, since AMD was initially a licensed second source, and Intel thought you couldn’t implement the Pentium instruction set without violating its patents.
What clearly is subject to copyright is the documentation describing the instruction set and its semantics.
Usually these patents are written such that it’s difficult or impossible to implement the covered portions of the instruction set without violating the patent, but that’s by no means guaranteed.