I've got 3 Linksys nodes running V3 firmware, and they all are talking to each other just fine. I've got a TP-LINK WR703N running OpenWRT that I'm trying to to get to connect to the mesh as well, and I have it to the point where it can see and is seen by the Linksys nodes, even shows up in the list of other nodes, but is unable to communicate with them. I gave the TP-LINK node an address of 10.234.106.6, which is consistent with the last half of the wifi mac address of that node. I know I won't get the nice interface on that node that I get on the true BBHN nodes, but I'd like to get it working, especially since that router is physically tiny, and can be set to a much higher power level. It would be really nice if there were a package to just add BBHN to an OpenWRT node. Once I have this figured out, I might try putting one together...

Have you considered the Ubiquiti nodes and maybe helping out with them over the TP-Link?

Ubiquiti devices are already ready to mount outside, an issue the Linsksys and the tplink you suggest both suffer at not being ready to go outdoors. The 4mb of flash is also a limiter (we already hit issues with 4mb being too small with Linksys). In addition I see a lot of hardware hacking needed to add external antennas, etc that the TP-Link device in question would quickly require more time and effort  cost than other solutions. 

We are looking to see additional hardware lines, but I'm not sure that this device would pass muster to live up to near, or even better exceed, what we have with Ubiquiti devices.

There is a bit more to it currently than just the web UI, it's a combinations of external packages (including custom patches), kernel patches, the GUI, and hardware specific customization in the GUI for each device to be sure accurate information is displayed ( if you don't mind inaccurate info about RF power for example this may not apply to you or if the device accurately reports all info ) 

I found out the hard way myself when I though "oh I'll dump it on a single Ubiquiti and be done fast maybe a small tweak or two" has turned into a year of tracking down each device because there are minor differences in each and the the occasional change even in the same series of device also comes up.

Oh heads up, we found the Rocket and NanoStation work better on receive than Bullet and AirGrid because they are MIMO instead of single input (allows them to pickup signals that may have rotated on travel).