ok, and now i think i have quite an interesting empirical evidence. do not want to do more tests on it for now, but - as i have flashed in an arducopter .hex file with betaflight - i was able to press DFU button on the kakute board and it went into the DFU mode with no issues and i just flashed back betaflight into it.
i do suspect that if one tried to flash new or altered .apj file with MP into Kakute - something in it goes kaput and board stops entering into DFU mode upon pressing a button - it has happened to my new AIO board that i also was able initially to flash into the arducopter and back into the betaflight.
so, if one only flashes .hex file it seems to work and this way it can be flashed back and forth if you want to compare how model will work on different code.
when you flash it - make sure to solder RCIN to the uart 6 RX. uart6 TX is also active and can be used for one way out - you can set it to pump out telemetry or anything that is a one way TX stream.
i am still having issues with uart7 for ESC telem - but will test more this weekend. it should work.
LED is not used. buzzer produces proper tones but will probably whistle upon power up until code loads as bootloader was never adjusted to put that pin into high state.