When U2 announced the Joshua Tree Tour 2017, all was silent on the Australian and New Zealand fronts. It is no longer.
We can report that multiple stadiums are negotiating with Live Nation about major concert events in Australia and New Zealand. U2 are a likely candidate to be the band in question, because other stadium-level Live Nation acts have either toured recently (e.g. Coldplay) or have announced forthcoming dates (e.g. Adele). It is possible, however, that these negotiations may pertain to another act, so do not raise your hopes too high just yet.
In Australia, Etihad Stadium in Melbourne is in discussions about a major concert event in November 2017. Similar conversations have occurred with Suncorp Stadium in Brisbane and with Sydney Olympic Park (which could mean ANZ Stadium or the nearby Spotless Stadium). The new Perth Stadium is very keen for a significant opening event to precede the commencement of regular sporting events there with the 2018 Australian rules football season. U2 are one of the few bands who could command a sell-out at this significant 60,000-seater venue.
Meanwhile, in New Zealand, Auckland's Mt Smart Stadium has an undisclosed event booked for November. At the moment we have no rumours for other venues in New Zealand.
These venues are those that U2 played on the 360 Tour, or in the case of Perth is the venue they would play once the new stadium is open to supersede Subiaco. Hence, these rumours are plausible. But as noted they could pertain to another major touring act, not U2. They are also very preliminary discussions subject to change. It remains very possible that any tour, if it happens, could instead take place in 2018.
It should go without saying that we have no information whether these shows, if they are U2, would be part of the Joshua Tree Tour or represent a resumption of the Innocence + Experience Tour. Word on the street is that the indoor form of the IE Tour has not come to Australasia because of how many shows would be required to satisfy demand and problems with fitting the stage into some arenas. Make of that what you will.