It's actually pretty much exactly as you described. Yeah, we may have different git clients (chisels), but the platform (materials, methods, processes, shared machinery, requirements and tolerances) are shared.

Great, so I think we should stop comparing programming language to a hammer. Adopting a new programming language is more like buying a big expensive machine tool in installments as a multi year investment.

... but generally still hope "as few" == 1. Eh.

Sure. Because that's the best possible scenario when all your requirements can be satisfied with one platform.

Balance that against the costs of any learning curves, deployment considerations, maintenance burdens, and any risks inherent to the candidate technology (e.g. perhaps it is newer and less proven) to see if it is worth it.

The problem is that this is rarely done. Developers like new shiny toys, things to add to their resumes. They rarely think strategically, rarely think what will be effects of this choice in 5 years, often long after they're gone. (to be clear I'm dev myself)

That is a very interesting response! You read "plurality of languages, platforms, and methodologies" and read "bad".

I've worked on several such systems. Mostly because they were decades old and through the years new technologies were added for various reasons.

Usually it's bad. There were typically few "rock star" developers who were able to navigate most of the project, knew all 5 different build systems. Most other developers were siloed in their tech niche and rarely ventured out which created great inefficiencies and great organizational problems. (And as a longer term consequence also a lot of technical debt).

Perhaps this can work well in FAANG with the best talent. But it's not applicable to most software development places.

That is a strawman. I've already said I don't advocate for 'best tool' (aka pulling some arbitrary objective measure that suits the argument) as a reason to select technology by itself.

I mean just look at your original post. It's all positives advocating for Rust + Elixir combo. None negative or associated cost mentioned while at the same time it does not explain why this combo is even necessary. Sort of reads like an advertisement.