SPI control for the 5.8g vtx would be boss, and have a huge upside.
The channel switch code is already avail, as the Industry seems to have standardized on Richwave rtc6705, and https://github.com/sheaivey/rx5808-pro-diversity or similar have the SPI mapping.
Weight weinies can use 2g vtx, and still choose 40 channels
All old 8 and 32 channels vtx could be upgraded to OSD channel switching (or choose ch via dronin ground station, or blind interface, looping through preset favorites)
Lots of AIO or toys would have the experience greatly improved, and these days complete products are far cheaper than parts.
This is $22 and it's a 720p recorder, with rich wave 5.8 200mw (nominal) vtx, but it's set to one channel only.
Recording quality is better than an 808 # camera which cost more, and FPV latency is OK.
(Spare part x252, banggood)