Honestly Donny.., I've always said in the past that it would be great to combine the two.., but I've changed my mind on that one.
I don't want them combined because the price on a keyboard like a Motif XS, Roland Fantom-G, and a Korg M-3 with arranger functions would be FREAKING SKY HIGH!
ALL the keyboard makers pinch the hell out of the arranger market in terms of price--that's not secret either.  The price difference is unreal.  They start combining these two keyboards (completely).., we'll almost certainly see a price tag of $4,500+ on the 61 key models.
They can't do it for several reasons..., at least not any time soon.  They'll lose a huge chunk of their market on BOTH sides of the fence.  Di-hard synth junkies don't want arranger functions.., and there are a lot of di-hard arranger players who don't want the complexity of a workstation mixed with their arrangers.
You'd be surprised at what people are saying about the price of a Tyros 3 on other forums compared to the Motif XS and other workstations.  Same goes for the other makers arranger line too.
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GEAR:  Yamaha MOXF-6, Casio MZX-500, Roland Juno-Di, M-Audio Venom, Roland RS-70, Yamaha PSR S700, M-Audio Axiom Pro-61 (Midi Controller).  SOFTWARE:  Mixcraft-7, PowerTracks Pro Audio 2013, Beat Thang Virtual, Dimension Le.