Well the only Haswell Macs are:

Macbook Air Mid 2013
iMac Late 2013
Retina Macbook Pro Late 2013

We could do with someone with a 2013 MBA to verify, but I'm pretty sure this is the exact set of people who are having issues. Furthermore, unless we have a 2013 MBA to test, I'm not convinced  `Hardware::CPU.extmodel` will be any different on 2013 MBA's from the other two models anyway. 

Bottom line - unless someone can enlighten us on the precise definition of `extmodel` I'd be wary of using it in any kind of discriminative manner.