If you read the -current man page for
ath(4), you will see WPA mentioned only in regards to two chipsets that can conduct cryptographic operations, and that the driver does not yet support WPA.
The PCI driver for ath(4) has not been updated in 5 months.
The chipset management software for ath(4) was updated several times, approximately four months ago, to add software crypto to support WPA and WPA2.
Note that all of these updates are in -current.
Since the driver has not been updated, it appears to me that development is not yet complete.