This up conversion can still make sense even if the interest rates don’t go down as with the 800k/5% mortgage, a larger portion of your monthly payment is made

This up conversion can still make sense even if the interest rates don’t go down as with the 800k/5% mortgage, a larger portion of your monthly payment is made up of interest, thus also your tax bonus is higher and in net terms you can end up ahead even in time horizon of 20+ years before the down conversion.