While there is no new Wi-Fi standard, that does not mean there are no new technologies coming out of 802.11ac. We have not yet reached all the potential from ac. The biggest is MU-MIMO and this one is going to take a while to catch up to because it is incredibly complex and requires both the router and the devices to support MU-MIMO. You'll see this coming soon as part of the 802.11AC wave 2 routers, some were already announced last week with 4x4 antennas setups (AC can go up to 8x8 IIRC, this won't happen for a few years because it is difficult to even do 4x4 at the moment). Dlink is supposed to have a USB-3 adapter with 3x3 out by now but no news yet.
With MU-MIMO, (multiple user, multiple input and multiple output), the router can dedicate antennas to specific devices, which ensures the device gets the best performance consistently instead of the router switching between devices when sending data out. Without MU-MIMO, the router uses all the outgoing antennas (TX, transmitters) for one device at a time. Which means if you have 3-5 devices all getting data, they all must wait their turn. With MU-MIMO in 802.11ac routers with 4x4 setup, 4 devices will get dedicated TX antennas _pointed_ to them (beamforming) with no waiting. This means you'd see a reduction in latency as well as they don't have to wait for their turn.
Airport Extreme is currently at 3x3. I'd expect Apple to bump it to at least 4x4, heck they can go 8x8 if they figure it out. I don't think they're MU-MIMO capable at the moment, not likely given the age as MU-MIMO is starting to take off now.
There are some tricks where MU-MIMO routers can group non-MU-MIMO devices together to increase the performance, so you still get a benefit from MU-MIMO router even without having the devices that support it.
Hopefully, Apple will announce a 4x4 MU-MIMO compatible Airport Extreme soon but I think it might happen next year, not this year.