You arr right on the money. That is a great loan. IN 10 years you coul likely see a combination of higher rates and higher home prices. Having locked in at 6% the paper becomes cheap. Additionally accounting for inflation his 3000K payment in 40 years is equivalent to a $1500 payment or less in todays terms.
There is also nothing that stops him from prepaying the loan back or refinancing if we got into soem wierd situation where rates went to some ridiculous 4% range. The big thing here is making sure you have the cash to continue to make the payment.
Nice thing with this home loan is that in the enevt of job loss I believe there is deferrment and forbearanc ein the form of PMI that will cover the mortgage so even his payment is insured. It is a good loan.