I see the timing as "convenient" - Daddy problems and the non-event African holiday Haz No Idea and wife are on - close to zero interest . . . . and now going into cold weather times - roll out the "announcement" ..... I'm not seeing Windsor but maybe York ..... or Italy - presume the groom is Catholic
I do think it will be Windsor unless she doesn't want her grandparents to attend. Philip probably wouldn't go to York and definitely wouldn't go to Italy so if the Queen and Philip are to attend it will be at Windsor.
It could be in the private chapel rather than St George's though with no coverage of anyone arriving or leaving but I doubt that. I think it will be a mirror of Eugenie's.