I agree, there's a "hammer and nail" problem here, it's impressive though that he used Ghidra to RE some of the API calls that the Nest binaries are making after having got root access - according to some of what Cody has said in the Reddit thread and on his Discord channel.

I have been working on REing the hardware itself to write drivers directly - for example at https://sett.homes/blogs/updates/the-lcd-display-reverse-eng....

I am designing whole new PCBs that mount in the Nest so that we have 100% firmware control over the device... time will tell if we can do the same thing on the Linux OS that the Nest currently runs on, or if custom hardware will be needed because the OS has too much locked down