Anyway, IME capsicum vs pledge doesn't make much of a difference because seccomp already forces you into a specific sandbox architecture; after implementing that, adjusting the result to support the rest takes (relatively) little effort. So I think the difference in adoption is more because nobody has volunteered to do the work for capsicum (and keep it up to date etc.)
Strictly speaking, that's false, my hobby project chawan[1] supports capsicum :)
Anyway, IME capsicum vs pledge doesn't make much of a difference because seccomp already forces you into a specific sandbox architecture; after implementing that, adjusting the result to support the rest takes (relatively) little effort. So I think the difference in adoption is more because nobody has volunteered to do the work for capsicum (and keep it up to date etc.)
[1]: https://chawan.net