its out since Juny 2019.
Details you can find in the Releasenotes of the MPX Launcher or here
I think SRXL + is the new feature in this firmware (telemetry back via SRXL). but still no documentation for the new protocoll. i checking the mpx homepage weekly for new information about this feature.
And for people who are using gyro or flight controls the possibility to switch now between Srxl Ch12 and Ch16.