First of all, I am of the opinion that arrangers will never completely die away... Look, they are STILL making home organs, thirty years past their shelf life ... But the progress and innovation (and particularly the affordability) of arrangers will come to a grinding halt.

The trouble I see happening is that, while CERTAIN arranger aspects are being copied - the chord following, the primitive division triggering, etc., certain aspects of arranger ease are NOT. Specifically, the ease of triggering divisions (call them arps if you want) at any point in the music and having the machine figure out the best transitions. Currently, most loop WS's only allow you to trigger divisions on the beat or bar boundaries. An arranger is FAR more forgiving in allowing you to hit fills whenever YOU want, and it still keeps the beat going.

Most arrangers also use a very gig-orientated workflow... You can order things by songs, by beats, you can have alternate keyboard settings be called up just by the song...you can have your lyrics synced to the arps, you can have vocal harmony effects synced with the arps.

It is important to make WS users aware of some of the more gig usable features over at THEIR forums. Make them see how some of this stuff is REALLY handy on a gig, and you stand a chance of getting them behind the cry for the feature to be ported to the WS OS...