All additions to list of keyboard layouts made with ibus-setup have no effect, and after launching ibus-setup there is no trace of them.
Having iBus enabled in configuration.nix means having no other layout but English, regardless of services.xserver.layout. And I want layouts like Polish, French Canadian QWERTY, Russian Phonetic. I also want to enable uniemoji and some pinyin IME, although i think i already discovered some engines attribute that enables me to add them.
I may use nixos-unstable and am happy with continuing to.