It's almost a chicken and egg scenario.. do the routers come with AC support first or do the Macs?
To me, it seems logical that the router should first support 802.11ac before the computers, but for some reason (and I'm too lazy to look this up), I feel like previous generations of Macs have supported newer standards before their routers.
Nonetheless, I do believe we'll see an update to the express, extreme, and time capsules this summer. That's just my opinion, but it does make sense when considering the rumors of 2013 Macs supporting AC.