And here's the thing I really don't get: 

The loan is only worth it to the person taking out the loan, if he can earn 60 BTC in today's money from the tolls. If it's been 6 years and deflation in consumer prices was 10% per year, then you have to actually pay back the equivalent of 80 back-then BTC.

Who in the world would take that loan? That is madness.

And, now, imagine deflation is over 10%...

What am I missing here?