Qi charging is all about convenience – get home, grab a beer, throw a steak on the barbie and chuck the S4 on the charge pad. If you are interested in Qi read the iTWire article here.
Samsung offer the kit for US$90 which comprises the Qi charger base (compatible with any Qi enabled device in case you already have one) and a new back (black or white) (note this stops you using a flip cover).
The slide out backlit QWERTY keyboard is US$80 and pairs via Bluetooth with an expected battery life of 8 hours of use. The one drawback is it needs to be charged by the microUSB cable - it is not integrated to the Samsung battery/charging system.
Regardless it will sell very well.