Yep that's is it. I should have read that facet page in the doc (just used the wrong keyword for search months ago)

btw, I played a bit more with faceting, and it is actually (functionally) good !

Datasette is (going to be) the "mpv" of DBs : An open (in code and in extensibility) standard for reading them. And that plugins system is a godsend. I will certainly delve into it more.