Agreed... in fact, I think that keyboard has been announced: the CME VX series.
Here's a link to press release, pix & videos . This is supposed to be a "modular" keyboard with coming expansion cards for sound modules with sampling, analog synths, digital mixing and more. Plus, this keyboard is supposed to somehow use "styles" for accompaniment - quote: "VX also builds in many MIDI songs and accompaniment in different styles, including loop variation and chord change...". With built-in audio/MIDI over USB the CME's look like they're ready-made for use with laptops loaded with softsynths & sequencing programs (esp. as the first keyboard ever to offer motorized faders). Best of all, it comes in every keyboard size you could ask for and is supposed to be affordably priced. This could be where our hardware and software arranger threads finally merge.
The CME VX-series controllers are generating a lot of talk in the other keyboard forums and with it's built-in arranger functionality I think we'll be talking about them here too. Needless to say, Yamaha is involved on the distribution side.