I think we don’t need to worry so much about φ as it should never be outside the expected range of [-π/2, π/2], i.e. we can consider it to be erroneous for this to happen.

The reason we need to wrap λ is that it can often be outside [-π, π] in some real-world data, especially as some GIS software does this to work around the “antimeridian problem”.  So wrapping in the identity rotation case keeps everything consistent.  Looks like I added the wrapping in @514cdcf9 and @f9f4e265.

In summary, I think replacing d3_geo_equirectangular with d3_geo_rotationIdentity would be a good idea. :)