Apple does use Rust, though from job postings, we can infer it's more like network services than firmware.
Regardless though, I don't see how the implementation language of your firmware is locking you into a specific ecosystem, so this criticism seems misguided to me.
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What benefit would Apple get from this? They want you all in on an ecosystem they control.
EDIT: Thought OP was talking about writing iOS apps using Rust.
Apple does use Rust, though from job postings, we can infer it's more like network services than firmware.
Regardless though, I don't see how the implementation language of your firmware is locking you into a specific ecosystem, so this criticism seems misguided to me.