Sure, add a module to a workstation, you got a potent piece of gear. But adding the arranger module to another arranger doesn’t really make sense. And quite honestly, a FAR cheaper arranger module (like a BK7m) would be equally useful to add to a Kronos2 or Montage, etc. without any of that audio loop issues.

Although Ketron’s OS allows a huge range of chord types to have individual loops, it’s horribly expensive to record and edit them all and it takes up a massive amount of memory (I don’t know the load time for custom resources though) and really it’s only mostly a few jazz styles that have any chord choices beyond those simple maj/min/7th choices. And adding to a Ketron style would be impossible, you'd have to match your own guitar loops to the factory loops, match playing, guitar type and amplifier type, effects etc.. Impossible.

I would pair a BK7m with a WS in preference to a Ketron. It’s pretty easy to direct certain style tracks to play external gear, so the arranger engine could easily drive the WS’s best sounds and drumkits, plus run in sync with the WS)s own arpeggiators and audio grooves. And it can be found for under $1000 (usually very lightly used! 😂).

I think the decision for a pianist with a high end digital piano would be how well the chord recognition works with conventional pianistic playing, and again, afaik no one else has expanded past the archaic ‘three notes gets you a new chord’ to Roland’s ‘plus five notes before a new chord with sustain down’ that revolutionizes being able to get good chord recognition without crippling normal piano playing. So again, I’d probably pick the BK7m module, it has awesome jazz and standard styles that often sound close to audio, with none of the chord type drawbacks.

Or possibly just get the FP-E50 and live with the slightly inferior piano for the sake of arranger integration (although the E50’s arranger section is very stripped back and you can’t add legacy styles).

Modules are cool, but best added to non arranger keyboards. And seldom offer the ease of use that a dedicated arranger offers. For someone not happy with a Genos2 and not an expert pro-level player with a high technical skill level, I’d recommend giving them a miss!