I don't know the latency of SATA off the top of my head, but I would assume it would be less then that of Wi-Fi. With the way the OS currently controls hard drives, this proposal probably just won't work. Since this pretty much rules out an OS drive over Wi-Fi (lots of random reads), we could instead think of a NAS setup for mass storage. So we have a small NAS with Wi-Fi, with samba or NFS protocols, and use it as a storage drive.
Personally though, I don't mind having an internal SSD in my laptop (although it is a bit small, really should get a bigger one). I also don't mind cables for external storage drives. As for Wi-Fi, I usually have a hard time hitting the maximum bandwidth of my AP (where maximum bandwidth is slightly less then half the connection speed). Wi-Fi is also prone to interference. One interesting thing about the 802.11 ac spec is that it now supports channel bonding on upto eight channels, which severely limits the 5GHz band, which was supposed to take away all the congestion we have on 2.4GHz.
Personally though, I don't mind having an internal SSD in my laptop (although it is a bit small, really should get a bigger one). I also don't mind cables for external storage drives. As for Wi-Fi, I usually have a hard time hitting the maximum bandwidth of my AP (where maximum bandwidth is slightly less then half the connection speed). Wi-Fi is also prone to interference. One interesting thing about the 802.11 ac spec is that it now supports channel bonding on upto eight channels, which severely limits the 5GHz band, which was supposed to take away all the congestion we have on 2.4GHz.