If enough voices are available it would be great to be able to run both sequence A and B at the same time.
The way to enable it would be simple as such.
Create a sequence as normal.
Then press and hold the current sequence you're on then press the other sequence. If in record mode you will now be able to record the second sequence. If you want to go back to playing only one sequence simply press to select the sequence you want to hear.
Switching between both modes playing serially or consecutively should be easy.
If this is possible it would make sequencing more complex parts much easier, especially wider octave ranges without needing to use an external keyboard or resort to step sequencing.
Another advantage is you could make a simple reference sequence in A as a sort of metronome then record B while listening to A, then switch A off by playing B only or overdub onto A to make use of the extra sequence.
I would gladly sacrifice being able to A/B sequentially for the above described features.