For condo towers, things are mostly going to be OK even if no one is living in the unit. You pay your strata fees & the strata takes care of most of the things which become a problem simply due to the passage of time.
For single family detached, the value of the building is not a big deal. It's the dirt the building sits on that people are buying. Prices went up ~30% over the last year in Vancouver.
There are also buyers who think nothing of tearing down a relatively new building because it's not quite what they want.
As long as the city remains a place people wish to live, the dirt will retain value. Perhaps it goes down 50-80% - you can live on your land or you can use its cash flows to help cover your living expenses. As a safe-haven, it's not a bad option.
The price in CAD/USD/EUR/CNY/XBT is almost irrelevant to these owners.
The problematic purchasers in my view are the locals. Many are buying because the market is going up - "I'd better buy now or I'll never be able to afford it". In a falling market, that demand many not exist.
Though I also remain unconvinced that the foreign demand will remain strong in a falling market.
What's going on in Vancouver isn't sustainable in any traditional sense. But the market can also remain irrational longer than many can remain solvent.
I agree that the phenomenon of properties remaining vacant represents a failure. I'm curious what opportunities you think there are. I suspect that many of the opportunities would require regulatory changes to be viable, but I'm open to a different perspective.
Regarding Chinese people understanding capitalism, I suspect there's a very different view culturally. I'm told that the advertising for financial products is quite different - in North America we tend to expect a convervative branding. In China you'll see investments with more of a WeChat approach (including being actually promoted on WeChat). Property rights were recently codified in China - i.e. 2007 or 2008. Real estate is mostly only available as leasehold in China. There's a lot of people who recently became quite wealthy quite quickly. I think it's very likely that they have very different understandings of capitalism than North Americans, who also have a different understanding than Europeans.