Qantas will use the 787s to replace other aircraft serving Hong Kong, but overall frequency for Qantas between Australia and Hong Kong is not increasing.
Does that mean Qantas is deploying 787s and freeing up aircraft for more Asia expansion?
Qantas is using the 787 to replace 747 - yes, and no
A Qantas statement repeats the familiar line about the Dreamliner that "the more efficient aircraft gradually replaces the 747".
Looking at Qantas' post-peak schedule for Apr-2018 and Apr-2019, it appears the 787 replaces the 747 on Hong Kong. Qantas shifts from 21 weekly A330 flights and 7 weekly 747 flights to 20 weekly A330 flights and 8 weekly 787 flights.
Yet the matter is not so simple. Before the 787 Hong Kong announcement, Qantas was planning an all-A330 operation to Hong Kong for Apr-2019, with 28 weekly A330 flights.
Qantas Hong Kong weekly service plan: 2018-2019
Source: CAPA - Centre for Aviation and OAG
Qantas Hong Kong weekly aircraft plan: 2018-2019
Source: CAPA - Centre for Aviation and OAG
It is possible Qantas' Apr-2019 schedule, where there was an all-A330 operation, was preliminary, and merely a holding option until Qantas finalised route deployment plans.
Yet looking at Qantas' A330 flying plan: before the 787 Hong Kong announcement, for Apr-2019 Qantas was planning approximately 96 weekly long haul A330 flights (to Asia and Honolulu). This is in line with the 94-98 weekly long haul A330 flights Qantas has operated over the past year. Australia-New Zealand A330 flying has averaged 30-33 weekly flights.
So it seems that before the 787 Hong Kong announcement, Qantas' preliminary schedule was reasonable and could be flown with its existing fleet. This does not appear to be a base where the fleet was over-rostered and needed 787s to replace capacity that did not actually exist.
Qantas A330 international flying by market: 2017-2019
Source: CAPA - Centre for Aviation and OAG
Qantas appears to have surplus A330 capacity
So, it appears that Qantas has surplus A330 capacity amounting to eight weekly round-trips with an approximately nine hour flying block per direction. This is not insubstantial capacity; it equates to freeing up one A330 (and then some).
There could be many options and geographies for this capacity. Qantas may use the A330 capacity to replace a 747 elsewhere (they fly to ports that include Honolulu, San Francisco and Tokyo). Qantas was looking to open a new Perth-Johannesburg A330 service but dropped the plan over a dispute with Perth airport.
Qantas could also continue growing in Asia, where the airline has resumed flying to Beijing and Osaka, as well as having increased capacity elsewhere. Qantas could look to a new port - and an entirely new country - by opening a service to Seoul.