Until they add something expensive that YOU'VE got no use for, eh Donny?
Expecting an $800 harmonizer in a $1600 arranger seems optimistic, at best. FAR better to provide maybe an expansion slot, and allow the owner to chose what level of harmony (if any) they want... (or decent MIDI implementation to facilitate third party harmonizers).
This is the way to let inexpensive arrangers get better at their primary function, rather than keep them hobbled while the large part of their R&D gets blown on features that few use... (or inadequate quality for those that DO use them), IMO...