I can only agree completely with the previous poster.

The wording could have been "re-routing on any carrier at the first available opportunity" - but it doesn't say that.

"At the earliest opportunity" also is vague enough to allow the airline to NOT have to book on the first available flight - if, for example, a competitor decided to jack-up the prices in response to their competitor's woes. In general, most airlines will try to accommodate pax on their own or their partners/alliance flights - rather than immediately booking on a competitor airline that may only gain the pax a 5 or 10 minute advantage!

The fact of the matter is - when this article is being invoked, it means that the passenger won't be arriving at the time they were booked. They are already going to be delayed - but there is no requirement for the airline doing the rebooking to always and unavoidable choose the very first option that gets the pax there with the minimum amount of delay.

The only clear intention is that regulators intend for the passenger to reach their destination without having to pay extra or to arrange for that replacement ticket themselves.