You possibly have answered your own problem with this statement.
If one has a loan they can afford, then negative or positive equity becomes irrelevant. Many years ago there were caps on % total income which was used as loan repayments based on a notional higher interest rate (say 10%). This was used to back calculate the maximum loan amount which could be provided to the borrower.
If someone can’t afford a loan because the interest rates return to normal levels (6-7%), then either the lending institution didn’t follow responsible lending practices or the mortgagee is living beyond ther means due ro their other financial obligations or lifestyle choices. Other financial obligations could include maxing out a credit card which assessment is somewhat removed from the mortgage repayment requirements (it is based on capacity to repay a credit card debit not necessarily based on affordability).
30 year terms are possible in Australia but risky for the mortgage holder as they are most likely to pay considerably more than shorter fixed term or variable/fixed portions.
The difficulty with 30 year term is there can be significant penalties if a loan term is broken, including paying lost interest if interest rates at time of breaking are lower than the rate in the loan being broken. Thia amount can be significant and more so with longer loan terms.
Also, if ones financial situation changes, say has significant increase in take home income over tge 30 years, most fixed term loans don’t allow additional payments to facilitate the early discharge of the loan. Therefore the mortgage is locked into paying interest on the loan at a potentially higher interest rate for 30 years, rather than being able to make additional payments and discharge the loan earlier…saving considerable interest payments over the life of the loan.
I also understand that the US mortgage system is also very different to Australia whereby a mortgage can in effect hand back the keys to the financial institution if they can’t afford the loan or the property has negative equity and unlikely to become positive in the foreseeable future. In effect walking away from the property and loan. I am not sure if this is something we want in Australia.
The recent GFC was partly caused by US banking system as the instutions were not overly profitable had had limited capacity to cover bad/defaulting loans. Fortunately for Australia’s financial system, it is highly profitable and well capitalised which provides some buffer should there be a significant increase in bad loans here. I would prefer the situation here rather than having a financial system collapse which would affect everyone in Australia.
If interest rates do go down, individuals have a choice to either maintain pre-interest rate reduction repayments to provide a buffer/reduce their own loan risks or only pay the repayments based in the new lower interest rate.
When the later happens, it is seen as a financial windfall and the additional disposable income is spent. When interest rates then increase at some in the future, the pain is greater as one has to change their lifestyle to dind money to cover the additional ihterest payment. If one had foresight (and maybe common sense), this situation could very easily have been avoided.
This is a decision of the mortgage and they should (or should they?) be advised of the advantages/disadvantages. Maybe then the interest rates go down, a mortgage has to apply for the reduced interest repayments rather than it be an automatic adjustment by the bank. This wmay then force some to reconsider the potential windfall if the lending institution provided sufficient details at the time of the interest rate reduction to why it is recommended that repayments are maintained at the pre-interest reduction rate.