Also, to add another layer of caveat to dual 5ghz is that in every case there will have to be some minimum separation of the two 5Ghz radios. Figure maybe 80-160MHz of separation (better performance will be had with more separation), which means from a channel planning/AP topology perspective, you loose a great deal of flexibility AND available non-interfered channels.
So while you may see a peppering of APs where they are single 5Ghz to cover an area and there's 40-80Mhz channel separation between APs, you will start to see issues when both radios are doing 5Ghz because each radio still needs the same separation IN ADDITION to the internal separation. So you move from having ~24 non-overlapping channels to plan with, you automatically *and in best case* drop to 12, and likely more close to 8 (if you factor 160MHz separation for on-AP dual 5Ghz).
In short, there are very few use cases where dual-5Ghz will be advantageous, and so far we haven't seen anywhere close to 2x perfrmance gain (even when doing UNI1 and UNI3 on the same AP).