I currently have a Nexus 4 and a snapper sim (it was free- why not?) but can't use it to pay for snapper fares.

My understanding is that the nexus devices lack org.simalliance.openmobileapi.service which basically allows the nfc access to a secure element on the sim card. Instead, it has a secure element in the receiver chip used for nfc communication. This has been used for google wallet, which, being in NZ, is not that useful for me. Sadly, you can't just install the libraries due to lack of plain apdu access (see here)

It seems that Google is moving away from this (the new nexus 7 & 5 don't have the secure element enabled chip for the NFC communications), instead moving to an emulated card available to all.

It would be nice if Google enabled support for sim based secure elements (in which case the snapper sim should start to work), however, if not, there would now be another way - emulating one in the phone. This brings in the stumbling block of not having the secure element to work in - however, if Google wallet can work without one, I'm sure a new snapper app could be written in a similar manner. The advantage of this would be no special sim / and a larger pool of devices that could use it.

Not sure how long the lead time on a new app would be, or, if it's something Snapper is keen to create. It would mean it wouldn't be 2 degrees exclusive though as no special sim would be required.