I am not sure if asking FinCEN about interpretations will bring us further. I have no idea how vague official clarifications are in US, but in Poland You get 4 different (contradictory) official opinions and none of them tells You the answer to your questions. Provoking court decisions was always a slow but more reliable alternative.
You can seek an administrative ruling. Essentially it is a letter which requires FinCEN to provide specific written direction/clarification. While it isn't the "law", if FinCEN gives you an administrative ruling stating "x" it provides some measure of protection if they later change their mind.
I think we should request this administrative ruling as soon as possible to give at least "some measure of protection" to US businesses accepting BTC. Otherwise they will leave the BTC economy. I think we should try to convince FinCEN that a person/business who/that is converting his/its own BTC to (fiat) currency is a USER (not a transmitter or administrator). I think we could also accept that such transactions should be reported if they exceed a certain value (>$10,000) but this will be taken care of by the exchanges. They will report this.
The latest FinCEN guidelines allow BTC transactions in excess of $10,000 (worth of value) without any reporting (the transaction is public but I am sure FinCEN would like to know who is the owner of the transacted BTC). I doubt this will stay that way.
=> We can expect modifications of the FinCEN guidelines sooner or later.