I don't know if a MacBook Air SSD has ever been put in an AirPort Extreme slot. I am not sure if the connectors for each one are physically the same. (actually based on photos the airport extreme has more contacts and is slightly wider). I have seen someone successfully install a hard drive in an AirPort extreme slot using Mini PCIe
http://www.xlr8yourmac.com/systems/mini_esata_card_mod/macmini_estatacard_mod.html
but I do not think you could fit the SSD in as it is rather long and if you did I don't think it would work.
Hope this Helps
(I guess we will wait for mayer)