Don't get me wrong. It's a KILLER workstation, and live VSTi player. And I LOVE the huge touchscreen.
But as an arranger, it will be no more useful than the MS.
And as a WS, you have to be aware that the 'empty box' concept is only as good as you can afford to make it, combined with the skill you have to set it up.
I think, unless one of the majors goes 'soft' (think Kronos with a PA3X engine), there will never be a decent soft arranger. At least, never as good as the current hardware ones. Too many things have to play nice with each other for it to work. Only the majors have the resources to do this, and they are probably making too much money off of hardware arrangers to slit their own throats!
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An arranger is just a tool. What matters is what you build with it..!