I think you are starting to realize some of the limitations that 'live loop' performances are going to bring to arranger usage, Rory.
300MB does not go very far on a loop library, and anyone that has worked extensively on loop-based audio production knows how difficult it is to change a loop into something it is not.... Time-sliced drum loops are one thing, you seldom need to edit them much, but a guitar or bass loop library? Not a lot of wiggle room there...
For as limited a project as Steinberg's original Virtual Guitarist (which only recognizes a few chord types) it uses over 1.5GB of samples. Do the math.....
I think that what we are going to see in the new Ketron are a few (Ketron say 60 styles, but how many of them use the same loops?) wonderful styles with very little customization of the loop elements, which will gradually get repetitive, especially if they are SO much better than your 'normal' styles that you tend to use them as much as possible.
And if they stream from HD (not stated in the info), I am still unconvinced of the good sense and reliability in constantly streaming audio files off of a HD that is in a device being constantly pounded on!
Having heard some EXTREMELY realistic guitar styles on T2s, and drum sounds from G70s, etc., I think that live loops, while initially impressive, don't offer anywhere near the customization and new style options that a REALLY good sample library and associated MIDI performances can give you. It just seems a waste to have over 300MB of ROM, and burn most of it on a few loops.
If your style needs mesh closely with the provided 'live loops', you may be OK, but for players with wide stylistic ranges, or non-standard (let's be blunt and just say 'non-nursing-home) styles, you may have a harder time making this new technology work. But imagine how realistic a 300MB drum sample library could get. Roland and Yamaha get some VERY realistic sounding drums from FAR less ROM than that....
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An arranger is just a tool. What matters is what you build with it..!