I had noted the lack of updates as well. The only explanation that I can think of is that there is not a lot of work being done on the v6, and the older versions are no longer available.
There are two major works for the v6:
1 - Reed N's software update that fixes a number of issues with the stock software, yet retains the stock display.
2 - The replacement of the stock display with a Nextion display and then update all software to the last version from KD8CEC.
The spurs and harmonics were fixed in the v5.
Including the case as an option made the case market diminish
The only major issue not covered has been the low transmit power on SSB due to the Boafeng mic.
There would be interest in adding extra display functions, like a panadapter and maybe some DSP for CW, however, none of that has caught on, even with the material from KD8CEC.
The other area not to get much traffic is upgrading the Nano to allow for more functions. This would be something that I would be interested in. There is a Teensy upgrade available. I have not seen any traffic on what has been done with it.
It seems like the major traffic has moved to QRP-Labs as the uSDX effort.
These are just my observations monitoring the Groups.io feeds for the three threads: