While the Motion+ is capable of producing frequencies as low as 50hz, it can only produce the low frequencies in a very limited amount. If there was an option to push it, the speaker could be damaged from being driven past it’s physical limits. So the lowest slider in the custom EQ is 80hz because it can be safely increased without any risk, while still offering plenty of low end.
While the Motion+ is capable of producing high frequencies up to 40khz, this is only under the condition that the playback device is using the aptX bluetooth codec, and the content being played actually contains audio recorded up to such a high frequency. The highest slider is only 12khz because most audio is not above this point, so adjusting anything higher would most likely not make a noticeable difference.
There will not be an update due to the limitations described above.
I hope I have answered your questions correctly