Housing can not be both affordable AND an investment. Interest rates need to rise, and soon.
I'm not sure you're entirely correct. A lot of people plan on downsizing their housing when they reach retirement age - Move somewhere smaller because you don't need to accommodate the kids any more, and further out of an urban center because you don't need to commute any more. This is a net positive - It frees up more valuable real estate in urban centers for working-age citizens to utilize, and extracts capital fro…
However, that is not really a good description of the property investment the OP was referring to.
The OP was describing the situation where one individual owns many properties for the sake of investment.
It is that scenario it is the investor demand for properties that is driving up the property price making them unaffordable.
What's worse is this situation is self-inflating.
As a property investor with a handful of properties, you're in a good position to go to the bank, get a further loan to buy yet another property.
That then drives up the property price, which drives up value of your existing property assets, which then allows you to get an additional loan for yet another property.
This also means, people without that collateral backing have a much harder time getting their first property and when they do they pay a much higher price.
That bubble will continue to grow while interest rates remains low.