Yes @marcosc I thikn it is stalled And I think it would be a useful spec, although it is not in the current WebPlat charter.
But for now it might be most sensible to move it to WICG, assuming the annotations WG agrees - it's in their charter.
As well as handling endless scrolling search, it would probably be helpful of e.g. editing systems could generate an in-page search rather than reimplementing it, in the case where the text actually is all in the DOM but you want to find e.g.
/\<h.\>/ as a way to search for the headings when you're editing…