Did the kext swap and it appears to work (at least being reported correctly), however, it seems to introduce a bug with 5 Ghz Wi-Fi that is being reported for other Yosemite users on rMBP, etc. Similar to an issue I was seeing with iOS 8 on my iPad.
Symptoms are Safari acting sluggish, etc. You can ping an address and watch the wireless drop while the issue is occurring. Various applications will start to hang as well and cause general system instability.
I've seen this occur with 3 different routers on my iPad, so its definitely something that Apple seems to have introduced. Just be on the lookout for it if you enable this. Keeping the kext file stock and it doesn't occur with the CAX card. So it looks like something specific in the BRCM4360.kext, IMO anyways.
Edit: Even 2.4Ghz isn't perfect, but it's quite a bit better. Seems to drop after I attempt to do some handoffs a few times.