"Programming a 144-computer chip to minimize power" - Chuck Moore (2013)

It's really not. This isn't a difference of opinion that looks like "well some thing x is better at doing y than z" It's a fundamental disagreement on the purpose and practice of the language. For regular Forth users, the high and low level sit together with Forth, you don't experience a sense of any kind of "layers" of abstraction over the fundamentals of what the machine is and does. One can dispute whether Forth has this property, but it's really not an overstatement to say that regular Forth users feel this sense deeply and share this subjective experience. The capabilities of processors change a ton over time, which is the most damning aspect of ANS Forth, it is simply outdated ! -- The "major forths" you speak of are exactly what is antithetical to the general forth philosophy of implementing only what is necessary above the lowest level. Even the term "major forth" really speaks to the bias that popular programming languages and their users have. And there's a really good reason for this, standard Forth words really just don't make any sense unless they give you access to the hardware in a way that cross platform software is largely antithetical to. Cross platform components in software fundamentally act as either a service to a platform layer or otherwise provide an abstracted interface to a varying implementations. The whole point of a language like Forth is to turn the lights on, to play the audio and to drive the car. Chuck was wholly aware of higher level systems

Ultra low power processors exist: "GreenArrays is shipping its 144-core asynchronous chip that needs little energy (7 pJ/inst). Idle cores use no power (100 nW). Active ones (4 mW) run fast (666 Mips), then wait for communication (idle). Tight coding to minimize instructions executed will minimize power. The programmer can also reduce instruction fetches, transistor switching and duty cycle. Chuck Moore GreenArrays, Inc." Source: this video They just are not widely used because ARM and similar processors offer much more computational power and people are happy charging their devices every day or so.

"I always considered that size and speed were important for amateurs. But in the modern context, there's only three parameters that matter: power, power, and power." --Chuck Moore this video

GreenArrays have really cool chip that boasts "the most power efficient per instruction executed" when they released it. On the order of picojoules per cycle IIRC. The chip has 144 independent computers (not processors -> computers) The inventor of the Forth programming language, Chuck Moore, developed it, and is designed to execute with this parallel model in mind. A parallel Brainfuck system might be a cool project to port over to this platform. link Here is a talk given at Strange Loop by Chuck: this video

Wouldn't that all depend on how much energy is used for computing, and how much for fetching and storing the bits involved? If the requirements involve slow computation with extremely long-term storage, perhaps mechanical computing can theoretically have an advantage. Then again, Chuck Moore's GA144 shows there's still plenty of room when it comes to optimizing electron-based computing for those kind of extreme scenarios as well. [0] this video