On a later date (Article 8 (1) (c)).

Of course, Art. 8 (1) b. refers to rerouting "at the earliest opportunity", but I don't seriously believe that, when informed of the cancellation of a sector planned for, say, January 2023, one can reasonably invoke Art. 8 (1) b to obtain a ticket departing today (as an extreme example) without triggering a re-price.

When informed in advance of a cancellation, there should be sufficient leeway to change the day of travel; but I don't really see that it would allow you to make such a drastic change as, for example, bringing the trip forward by several months (even if delaying the trip by several months would be acceptable).