What do you hedge your 100 year financial vehicle with? AFAIK there just isn’t anything that allows you to hedge against interest rates 50 years in the future.

So while this probably works out (especially if there is high inflation or high interest rates for some of the 100 years), I think the upside as a borrower is very limited, especially if this ends up being popular (if interest rates fall to 1% next year and stay there for 100 years, you didn’t get a great deal…you most likely just have a CD in a bancrupt institution).