Would work... but to bond we would need another device (switch or routerboard) to bond through so costs do go up with additional rb922 and whatever they Bond through. Also if one radio slows down (interference) it will slow the bond as a whole down (unless you can do an unbalanced Bond... I've only ever used lacp where each bonded interface needs to run at the same speed, so I'm not sure an unbalanced Bond is possible... time to read more). But that is a valid and known to work configuration without taking up anymore spectrum or resources.
As a side note I did think of using the 2 radios via nv2 and bonded internally in the rb922., but the 500mw vs the 1600mw would give a different speed... but if they were able of be bonded unbalanced, then that may also work, but more of a chance of lower speeds...
If only they made a gigabit powerbox, installation would be easy
Why bother with those additional wlan cards, just get 4x RB922UAGS-5HPacT-NM, 2 on each side, connect antenas as you previously mentioned, than do interface bonding.You will get 2000mbps link.If you want guarantee 1000 mbps both ways you can set up some Queue to limit it to 1000mbit one way, or do even better balance where it drops lets say download in case more upload was requested.
EDIT:Actualy you dont even need any kind of queues, just do bonding on some MT switch and the exit port will automatically get max 1gb both ways, and bonding interface can do its own balancing to maintain 1gb full duplex(combining 2x 1gb links).
Just my opinion.