While I agree that a keyboardist should be versatile on all kinds of keyboards, I disagree about the search for the best - even a custom keyboard. The reason for the possibility of a "custom keyboard" is not about finding a solution to fill in a gap in technique and skill but to fulfill a particular need of a keyboardist which tend to be rather personal.
A keyboardist differs from other instrumentalist in that he plays more than one "instrument" - so different functions of the keyboard helps in his everyday playing (or for me - sequencing as well). I may not need a breath-controller input, but faders are indispensable. Although I can use both mod wheel and joystick controllers, I still prefer the mod wheels for controlling samples because of the way the crossfading are programmed. Although weighted and semi-wieghted keys are both OK for me, weighted keys give me more control and expression on piano sounds while the unweighted gives me more control on Hammond type of sounds. It is difficult to play repeated demisemiquavers on a single note fast on a weighted keyboard (fingering 4,3,2,4,3,2,4,3,2 etc), a technique which is commonly used when playing the Hammond. These are all pretty individualised. So instead of having a load-full (or a room-full) of gears to fit all the needs of a keyboardist, why not have just one keyboard that has all the functions that keyboardist need and nothing that he doesn't need?
So, I believe that a keyboardist should be versatile. In fact, I try to get used to different types of keyboards (Korg, Yamaha, Roland, Kurzweil, Alesis, also different models) because sometimes I need to play them "on the spot" and don't have time to figure out how to call up a patch (depending on where I'm required to play them). But that shouldn't stop us from finding one that suits just us. Actually, I'm speaking more in terms of sequencing and programming than just live playing since we want ergonomics so as not to waste time and to quicken our work process.
Just my two cents.
