How's that gonna work in Heathrow fog then?
Because at 3.5° - under current rules - the system won't be anything better than Cat I; for Cat III: 3° shall be the angle of the GP and the angle of the GP shall be 3°. And I don't know of any ILS installation that has a 'set glidepath angle for the day' switch. Usually any change to GP parameters is subject to a thorough Flight Inspection - especially for Cat III installations.