It seems reasonable, but we need to not conflate niche with lacking-popularity (i.e. low usage).
Niche is about the environment, i.e. the problem domain.
Analogy to biology/ecology, grazing on mountain tops is a niche that is also unpopular (i.e. low usage), meanwhile pollination is a niche that is popular.
The problem domain for Rust to be useful is very large, across the programming ecosystem and across the programming ecosystem effort is put into increase accessibility for the less and less experienced (e.g. embedded, wasm, webservers, clis, etc). However, Rust might currently lack popularity (i.e. low usage).
The problem domain for Inline Asm to be useful is very small, typically by experts in narrow domains and across the programming ecosystem effort is put into decrease the need for inline asm (e.g. crypto, firmware, drivers, etc). It also happens to be unpopular, and is avoided as much as possible.
Summary, Rust is pragmatically niche, rather than theoretically niche, Inline Asm is theoretically niche, and also pragmatically niche.
Niche is about the environment, i.e. the problem domain.
Analogy to biology/ecology, grazing on mountain tops is a niche that is also unpopular (i.e. low usage), meanwhile pollination is a niche that is popular.
The problem domain for Rust to be useful is very large, across the programming ecosystem and across the programming ecosystem effort is put into increase accessibility for the less and less experienced (e.g. embedded, wasm, webservers, clis, etc). However, Rust might currently lack popularity (i.e. low usage).
The problem domain for Inline Asm to be useful is very small, typically by experts in narrow domains and across the programming ecosystem effort is put into decrease the need for inline asm (e.g. crypto, firmware, drivers, etc). It also happens to be unpopular, and is avoided as much as possible.
Summary, Rust is pragmatically niche, rather than theoretically niche, Inline Asm is theoretically niche, and also pragmatically niche.