Unifi 5.6.29 brought the EOL warning for Ubiquiti Unifi AP-ACv2 hardware:
Support for this device will end soon. This device will only be supported through November 6, 2018. After that any new firmware updates, including security updates, will not be released. This device will not be supported from controller version 5.7.0. If that or a newer controller is installed then any new configuration changes will not be provisioned.
To keep using this deprecated hardware, you MUST switch your Unifi LTS channel in
deb http://www.ubnt.com/downloads/unifi/debian unifi-5.6 ubiquiti
The replacement APs are smaller and use a different bracket since the new APs are circular. The replacements are only 1/3 to 1/2 the price of the Unifi AP-ACv2. Ubiquiti in-wall APs start at $99, excellent for improving coverage in hotels and dense office environments.
Many users in light to moderate use environments (home / small office) will use the AP-AC-Lite. The extra 2 dB of transmit power of the AP-AC-Pro will not allow one to use less APs. The limiting factor is more typically MIMO channels and clear channels.
The AP-AC-Pro allows high user count in a given environment due to 3x3 MIMO instead of AP-AC-Lite 2x2 MIMO.