Are there plans to post Firmware for Ubiquiti M3 or M365 devices

Beta would be a strong term, It realistically isn't even in Alpha support yet, there has been experimentation but no active effort on the hardware yet to date.

The 3.4ghz band (m3's) have a feature ticket AREDN->ticket:52 but is dependent upon a few other items. It has been delayed in the past by other issues that have come up that had to take priority (stability and security). The M365's haven't seen much looking into because its licensed site only band (outside of Part 97) and the radios have very very sharp filtering meaning they can not be pulled into the ham bands because the frontend is dead.

Its certainly on the list of bands that I would like to see supported. Though its usefulness may actually be limited. http://www.ntia.doc.gov/files/ntia/publications/ntia99-361.pdf (note: this document was written regarding the Navy interfering with the civilian world but one can extract the data to understand how we would interfere with the DoD primary user)

All of SOCAL coastal (including my home development test lab) and other navy port areas, along with ANY area that has jet fighters (read as in 100% of the USA) is considered part of DoD 3.4ghz RADAR band (Ship to Air, and Air to Air and Air to Ground) and wifi would likely as I understand interfere with the DoD radars. Quoting: "The highly mobile nature and National Defense mission of naval radars extend the potential shipboard radar operational areas to include ALL waters and thereby ALL coastal areas of the United States and Possessions." (emphasis added)  and "Airborne operations of radar systems in this band can occur anywhere in the US&P. Figure 2 shows the existing nominal military operating areas (MOAs), restricted areas (RAs), and military training routes (MTRs) where military flights are most likely, although specific missions may require unscheduled airborne radar system operations in this band anywhere in the US&P at anytime, day or night. Note that at nominal altitudes of 30 thousand feet, the radio line-of-sight extends for hundreds of kilometers beyond the areas and routes shown in Figure 2" (emphasis added)

This is another reason that other tickets have been allowed to take priority over this feature as it may turn out to not be that useable in the real world (Not sure if you have had issue with 1.2GHz Radar yet but ive seen my fellow operators pounded by the FAA on this one recently and its a similar technology on 3.4GHz)

Actual usage may not be as bad as feared for Air to Ground making the band still useful, that is a subject each operator would need to speak to their local federal installations about their radio usage to know for sure.

See the beta test announcement.

http://www.aredn.org/content/beta-test-announcement