One of the criticisms levelled at pianos such as the Stuart which feature keys above and below the ‘standard’ 88-key range (A1-C8) is that there is little or no music written for such a range, therefore why worry about the extra keys.
In fact, pianos with extended ranges (normally the bass, but also the treble) have been known since the mid-1800’s. Henri Pape (the inventor of the overstrung piano) made an eight octave piano from F0 to F8 above the usual C8 around 1840. And in the same period, Johann Peter Pixis wrote a piece with the use of this high F. (I haven’t been able to locate this yet). Henri Herz (inventor of the whippen spring, pianist, composer and piano builder) produced a concert grand of 90 keys from G0 to C8. And there are others. From a compositional viewpoint, Busoni, Bartok in a concerto, Dukas in his famous Sonate, Maurice Ohanna in one of his 24 Préludes, Maurice Ravel in "Barque sur l'océan" have used an expanded keyboard.
The 102-note Stuart piano (C0-F8) is the only full-range piano currently being manufactured – full range in the sense that this range is seen as the (current) practical limit for an acoustic piano from both a technical and acoustic viewpoint.
Writing music for such an extended range is actually now much more accessible than it used to be given the plethora of electronic keyboards now available. Indeed, it is now possible to produce a ‘piano’ sound over the entire human auditory range – certainly a much greater range than any acoustic piano would be able to do. So, technically, one can write for any range one wishes to take.
But then, what is the next step? How to perform it, and how does it sound? All electronic keyboards I have seen have 88-notes or less, so as a live performance instrument the entire 102-note range of the Stuart is not available. It is certainly possible to transpose the entire keyboard up or down as much as you like, so whilst the 102-note range is covered, only 88 notes of that range are available at any one time. If the music is notated electronically, then MIDI playback can play as great a range as is physically possible on such a keyboard, but you lack the live performance dynamics.
There is another issue which really strikes at the heart of what is being attempted here. An electronic instrument will normally transpose by applying an appropriate frequency modification to the patch stored in the instrument. Even more sophisticated systems will need to provide some sort of predictive algorithm to try to produce a note with the ‘right’ frequency response. And that is where the problem lies – because the actual frequency response of the very low notes on an acoustic piano bears no resemblance to the higher notes which would be used as a template to be modified in an electronic piano, i.e. the FAT (Frequency/Amplitude/Time) envelopes are totally different.
This means that not only is the sound going to be invalid, but also the interactions of that sound with other frequencies will also be invalid – so you will never get the genuine sound of an acoustic piano, and you will never get the FAT of the total piano experience with an electronic instrument.
So, yes, music can be written for extended range pianos. Bear in mind, however, that it just not a case of writing the notes – anyone can do that. It is critical in this day and age to write for the sound of the instrument – the attack, the decay, the frequency envelope. And in live performance, where the pianist needs to be in total control of mind, body and instrument – an electronic instrument just will not do. It has to be acoustic, and at this time, the Stuart piano is the only piano which is specifically designed for such a task.