The Chord Sequencer, on Roland arrangers for about ten years (up to the G1000) was a system where, completely without interrupting normal arranger operation, the CS could record just the chord changes you play over any length of bars (either with or without the variation and fill changes you used) and seamlessly start playing them back at any time, and seamlessly go back to live chord input...

In other words, you could play the Intro, hit the CS record button, play a verse and chorus (or head), hit CS play, and the CS would take over inputting the chords. You now have a hand free for bending solos, playing two handed piano, counter-melodies, even playing a different instrument, and all the while you still control exactly when fills and variation changes happen, even change styles. And hit CS stop, the arranger still keeps going, allowing you to play a bridge, vamp, whatever, then hit CS start to go back to your Verse/Chorus/Head...

The only thing remotely similar to it is Ketron's Riff feature, which is preset chords, hence completely useless (sorry!), or Korg's Chord Recorder (can't remember the correct name for the feature) which is completely non-realtime - you have to input the chords in advance.

Roland's Chord Sequencer was the best 'third hand' feature any arranger ever had, and it's loss completely ruins the whole arranger experience for me.

First arranger manufacturer to reintroduce this feature gets my money, no questions asked...