802.11ac is an emerging standard from the IEEE which does not have Wi-Fi Alliance certification. The last Wi-Fi standard with certification was 802.11n, introduced in 2007. Regardless, Apple has already announced support for 802.11ac in some of their products, and third party products are available. You can expect less expensive product to launch by mid-2014.
If your home is already congested with numerous Wi-Fi devices competing for bandwidth then absolutely consider purchasing an ‘ac’ router. Some of the advantages include better performance, 5-gigahertz spectrum rather than the 2.4 gigahertz, and MU-MIMO technology for sending packets to multiple devices. Any 802.11ac product should be backwards compatible.