I don't think RI is a bond. Bond is a debt instrument and you don't loan anything to AWS when you purchase an RI. RI is a hedging instrument instead - you think that if you end up running an instance non-stop or near-non-stop, you are hedging against paying a full price. Hence, RI is more like an option.

Further parallels with options are: 1) your upfront payment is option premium; 2) your RI has time value which is always declining as time passes; 3) RI gives you a right, not obligation, to do something; 4) RIs have many series, each expiring at the same time, just like exchange-traded options that expire at predetermined times.

All in all, this is huge. Or even bigger than huge. It can enable certain things that were not possible before, and personally I am very excited about opportunities it will present and how it will re-shape public IaaS.