Regarding [1], Maybe we could show a 'show all sister wikis' button at the end of the sister project snippets list, so that the list expands to include the missing wikis (decision which to include is local consensus , like at [2])
[1] https://en.wikipedia.org/w/index.php?search=the+night+is+nigh&title=Special:Search
[2] https://en.wikipedia.org/wiki/Wikipedia:Village_pump_(policy)/Archive_135#RfC:_sister_projects_in_search_results
Based on the RfC that was completed on enwiki and it's follow-up, the consensus was that enwiki did not want all the sister projects to be displayed.
Also, based on another conversation on enwiki village pump, there are a number of folks who wanted to 'hide' the sister projects and a code snippet was provided to do that. I'm not sure that adding in another button or preference to show all the projects that enwiki didn't want in the first place would be a good idea.
However, all the sister projects that are available in the search results will show on all other language Wikipedias.