I wouldn't make such assumptions. Apple moved to gigabit ethernet ports long ago too, but the ATV still only has a 10/100 port.
The truth is (and nobody seems to believe), there is very little reason for Apple to add 802.11ac to the ATV. It will not improve performance (buffering speed or reliability) since your broadband internet is still the bottleneck (5-50 Mbps), whereas the current 802.11n already provides 150 Mbps. Also, 802.11n works in both 2.4 GHz and 5 GHz bands, while 802.11ac only works in the 5 GHz band (which has less interference but also less penetration through walls).
The only exception would be for AirPlay; 802.11ac may reduce latency.