Anyone expecting the T4 to be the last Tyros is going to be very surprised when the next Tyros comes out.
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Given that a few new sounds, a few new styles, and a couple of OS changes and blue lights is enough to warrant a model change, well, Yamaha can mine THAT vein for decades!
Ian will point out that Yamaha arranger users don't WANT radical change (and anyone that says differently must be a tiny minority) and what they are doing is EXACTLY what you all want... So bring on the T1000. That should probably be the 'terminator' of the line!
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Skynet rules!
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(Oops! Meant to say Yamaha!
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)