To make use of the built-in ATU on the 6K series whilst SWL one could use an antenna analyzer to find the impedance of the antenna at the shack end of the feedline. An API call to have the ATU match the complex conjugate (CC) would then 'tune' the antenna for out-of-ham-band listening. At my station, matching the antenna results in a +10dB signal gain. The SNR is unchanged (?) but matching would allow for weak signal SWL DXing.
Additionally, in-band tuning of the ATU could faster. The analyzer determines
antenna impedance, an API call sets the ATU rather than having the ATU search for the match. I believe the algorithm to set the ATU to the CC is not difficult.
Sounds like a very good idea as long one is within the tuning range of the tuner. Usually the relay-switching type tuner has limited SWR capabilities and one might not be able to wander very far outside the amateur bands if the antenna is a dipole or vertical tuned to a specific band. Also as the SWR gets higher and one is using coaxial cable, the losses of the coax rise abruptly.
That's why I purchased a Comet 250B antenna for broadband RX. I spend more time listening outside the ham bands than inside operating or listening.
This might mean that I would spend the money for an ATU just as a pre-selector for SWL assuming as Jim K6QE stated it's with in the tuning range of the ATU. With the SGC units they will cover 1.6 to 30 or 1.6 to 70 TX with RX improvements. I can take a 40 meter antenna on my mobile and with the SGC-237 at the base make it a usable 20, 15 etc... antenna and a Great 40 meter antenna. Not so with the ATU inside my TS-480 it will match the radio to the coax but the performance is even less that the SGC-237 at the base.
One down side is switching the measurement device in/out of the antenna ports but this can be worked out. Who knows perhaps there is enough h/w in the existing 6K radios to support this. The underlying support for pre-distortion is not that different I should think. Envelope tracking is a different beast and not supported.
API for CC matching would use the CC and frequency for the match as inputs. The return should be the actual matched impedance and perhaps the SWR, although the invoking program should be able to determine the SWR. A choice to perform the match or bypass the ATU would also have to be part of the logic.
Not all CC can be matched so the output parameter gives an indication of how bad the results would be and lets the invoking agent use / bypass the tuning unit.
FRS would not have to add any h/w just a couple of carefully crafted APIs.