The community-supported goland driver by Dan Cannon is so good that it's not worth writing a new driver. Over time we plan to adopt it under the official RethinkDB umbrella -- I should be able to talk to Dan about a collaboration soon.
It has a couple of things that I think could be better, in particular it could leverage go's native json support more. I have a few other ideas on this... you know where to find me though.
Regarding the json support the driver actually uses the native package however due to RethinkDBs use of psuedo-types an extra decoding step is needed and that is why GoRethink doesnt let you use json tags directly. Regarding your other ideas it would be great to discuss them.