There was actually good whitepaper before release ov R710, where this was dicussed.
I think it was named "using all tools we got" or something similar.
Interesting that Beamflex+ is in fact the only technology on market which can work together with MU MIMO. So it becomes only more important with wave 2...
Most important modification made in latest realisation of Beamflex+ in comparison with Wave 1 is that every Beamflex antenna (set of multiple elements) can be optimised separately in the same time for different clients when MU MIMO is used.
All other trechnologies (including Cisco Client Link and 802.11ac standard beamforming) use pair of antennas to get max theoretical 3 db gain, which decreases number of spacial streams or MU MIMO clients 2 times. 3db signal gain may provide 10% additional bandwidth, but loosing second spacial stream cuts performance 2 times. So probably 802.11ac standard beamforming and Cisco Clientlink will be never used (as they are not used in practice now), because even if they work, they benefits are heavily outweighted by 2x performance loss.
By the way, it makes sense to remind, that currently you can realise benefits of Wave2 in R710, as there is no clients supporting Wave 2 and even standard itself isn't yet officially complited. But as R710 is software defined, and all hardware dependencies are there already, it is a brilliant investment in future proof network -- any possible last-minute changes of standard will be implemented as firmware upgrade, but when new clients will come to network, performance will grow without any additional investments.
So if you thought about buying R700 - go for R710 without any reservations. For what it is providing, it is actually cheap.