With the universal Qi charging pads available for the N900 what is stopping us from adding a stripped NFC USB dongle onto the loop other than adding the data lines. It would require a custom scripted instance of host mode but definitely doable, maybe activated by some accelerometer detected gesture.
N9 users have had NFC from the start, what are they able to do other than link to a BT headset or maybe exchange contact details? There is this, http://talk.maemo.org/showthread.php?p=1291133
Not sure what mobile payment options we will have unless we can build a wrapper for an android app. Mass transit and door entry codes would all need the source algorithm to pass the encrytped challenge, again possibly requiring an Alien Dalvik type repackaging for large installations which is still being worked on, though perhaps if you know who is doing the lock programming the key seed might be available. Can smart cards be dumped if you have a physical connection programmer?
Of course the NFC could be added without a Qi charger though the special semi-permanent flush fit USB connector, antenna loop, and packaging makes adding the NFC much easier.
Since there would be no data pin short the Qi pad could have a RFID which could be used to send the N900 into the no-short charge mode for as long as it is on the pad.

Let me ask this another way, is there any point in adding NFC to the N900 without considering how to get the needed data I/O.