You could set a flag on your account to only allow people who you approve to hold your IOUs. That would avoid the scenario entirely. You could have a simple click through people go to in order to agree to your terms and gain the right to hold your IOUs. (Your IOUs can still ripple through people who aren't allowed to hold them.)
Still Ripple through! Nice detail, very nice. This stuff certainly conveys a sense of having been "thought through". Nice work.
I am a newb and may be totally off, but this is a lot like what it sounds like reading the wiki and the various threads. What makes it extra confusing is the parallel currency that is used to "pay" for our IOU transactions.
Try the other way around, too. This new cryptocurrency is a lot like bitcoin, but has all this extra-confusing currency-exchange and being-a-bank stuff that makes it extra-easy to exchange it for not only bitcoins but any other ecurrency, but even for fiat, apple dumplings, gold. or anything at all if you are gutsy enough, and risk-tolerant enough, to believe people will actually honour their IOUs.
"They" can say all they want that is is not a currency, until they are blue in the face and more, but just its actual functionality whatever the heck anyone calls it makes it work like one and its difference from all others in the system, as the native functionality, the native local currency, it works more like one for practical purposes than the IOUs even though the IOUs are more like 'normal fiat money" than it is. XRP is like "that most useable as a medium of exchange commodity, that naturally comes to be used as currency", the IOUs are all the fiats, that, if they have any value at all, derive their value from someone or some thing's "obligation" to make good on them.
So even if it is "a commodity" not "a currency" it is a "commodity" more like "gold", maybe more like "gold with built in antigravity to make it more convenient to hold and transport", while also being "already stamped into convenient assayed and measured form for convenient assessment".
In short if its not a currency, its something even better than currency that does the same job but better.
Oh wait, isn't there a word for that?
Oh yes, there is! It is "another type of bitcoin", a "proof of work -less bitcoin"!
-MarkM-