Software for building an 802.11ac AP?

[Adam McDougall]

Hello, a friend of mine is interested in building his own 802.11ac 
access point with a replaceable wifi module so he can save money on 
future upgrades by just swapping out the wifi module and possibly 
antenna. He was thinking to plug in a USB wifi radio but I was thinking 
minipcie would probably work just as well if not better.  Does anyone 
have any suggestions of software projects I could check out along the 
lines of openwrt so we don't need to work on a totally custom software 
build?  I was hoping to look at the supported hardware of such projects 
for clues on what kind of "embedded" hardware and radios he could buy 
to facilitate this.  Thanks!