A good example of additional function would be a LOAN system.
Simply Issue a Bond(either Zero Coupon or Fixed Rate depending on the desired payment framework of the loan), whose total total debt obligation is X. Then sell the Bond for X-I. I is then the
Interest, and X-I is the
Principal of the loan.
Note also that you now have the notion of credit worthiness. A loan is valued by it's risk, or the perceived ability for the debtor to pay back the loan. Thus there are also all sorts of possibilities to design credit rating systems based on practically anything. Running credit operations is profitable if done right. You could even securitize these loans and build a basis for something like a mutual fund. ie. The Bitcoin Development Mutual Fund.
The last section of the paper alludes to really a whole new vista for personal finance. Currently loans are highly regulated(in the US and Europe). For instance Prosper.com was torpedoed by the authorities. You have to wonder: why? America was built on alternative finance.
http://en.wikipedia.org/wiki/Early_American_currency , but with this tool you could for instance issue mortgages on the system, and you can own a piece of your neighbors mortgage, even use it as a kind of tender(as explained in the paper) for local commerce.
