the piano keyboard isn't a linear, one dimensional layout - you can constantly sliding in order to switch keys, reach accidentals, or facilitate technical runs.
The linear vs. spacial keyboard concept is not concerned with the lenth of the keys. One can construct piano keyboard with buttons.
Sliding along the key will get you into different tone. Uniformed can be made with 2 to 4 rows.
Jim's description is interesting, but I usually consider piano keyboard as two, one diatonic in the key of C and one pentatonic in the key of . Both playable on their own. I'm not a pianist, but having older dauther taking piano, and supervising her progress, I practiced her pieces for at least first 3 years, and paid much attention to the teaching methods. Otherwise, I can't play, but I can give advices
What instrument is that? It looks a hybrid melodica-clarinet....what is its tone like?
I will say that if you change the length of the keys, it's no longer the same keyboard, since the same physical gestures are not required to play it. So the length of the keys is of great importance.
Tallship is probably right - this topic should probably have its own thread, and we should probably all be practicing!