Multi generational is already popular, certainly in my area.

Houses and alterations and additions are getting smaller. Probably due to construction costs mainly, although some are mentioning sustainability and running costs as concerns.

To be honest I think the biggest boom industry is going to be in-fill development and re-aligning urban housing for mental health. I think the major projects are going to be in revitalising dead zones in urban area's and creating cosy apartments in places previously considered too small to bother with. There will be a huge push to developing shared green space, particularly in items like vertical and community gardens as these are necessary to prevent metro area's from feeling like ghetto's.

Australia isn't going to decentralise anytime soon, our entire economy is built up around three major cities and some smaller hub cities. The vast distances and lack of decent transport outside metro zones coupled with the prohibitivaly expensive idea of putting in dcent public transit will leave the urban planners scrabbling to retrofit the metro's we already have rather than build new ones. The obvious first major project would be linking Canberra to both Sydney and Melbourne via ulta fast rail links. That project has been on hold and debated my entire life (I"m 50 now) so I think it's safe to say its unlikely to happen. They will go for the easier option, cram more people into the urban zones we already have and keep the status quo.

Australia's cities are still very low density by world standards. Plenty of global developers would be happy to be involved in infill and repurpose developments here.