My ideal setup would be a single keyboard with 76 good keys and speakers (40 Watts shoudl be enough for personal monitoring or small room), under 40 lbs (preferrably less) in a light-weight metal case (titanium or magnesium alloy) for durability. It should contain arranger functions, ability to convert styles from all current models or convert MIDI or audio files to styles (take a portion of audio track and shift in in pitch and harmony with Variphrase-like techniques). Has to have a large hard disk (use what is available for laptops, e.g 100 GB 7200 RPM) to do digital recordings and store sample files. Sampling is not important (few of us know how to do samping well) but the ability to load standard format samples for playback is crucial - must allow expanding RAM to current standards (e.g. 512 MB minimum, up to 2GB). It has to have TRUE 128 note polyphony, and allow playback of audio/MP3 files from the disk.

Should have at least two individually controllables sets of outputs (one for mains, one for monitoring), and four inputs, at least one with XLR input, which allow using internal amplification and effects for a small combo (a guitar and two vocals). Any one channel should be routable to a good quality vocal harmonizer.
Also, a firewire or USB 2.0 output should send all of the solo, input, and arranger tracks out individually for multi-track digital recording on the PC. USB 2.0 master and slave connections shoudl allow connecting to the PC and/or a USB external storage device.

It should have a user friendly interface, a combination of Tyros and Roland Fantom (selection buttons UNDER the screen), and no touch-screens, please. If it has faders, they should be motorized (so that you can look at them and see the settings of the flutes or volume parts, instead of having to watch the screen as you adjust the settings). The user interface should have externally mappable buttons, so that you can add, say a USB PC keyboard, and map each button to a particular function, for more interactive single-button-push response.

Obviously, my ideal setup does not exist (perhaps a Mediastation, though I have never seen or heard it, so can not judge the sounds/styles capabilities). It is also not likely that any one manufacturer will create it.

A more likely scenario is that someone will come up with an expandable controller in an agreed form factor, so that you can have have good quality keys and drop in, say, ketron MIDJAY for arranger functions, and, for example, Yamaha Motif XRack for sounds, and still end up having to carry a single physical device (not a bunch of rack-mounted gear which is hard to reach and a chore to interconnect with loose wires every time you set up.

Regards,
Alex