I, like you, have or had a WK8 and one of my reason for getting rid of it were the keys (my father now has this keyboard and I got the X1).
I dont think its possible to change the keys especially from one brand to another. if it was the same company then maybe so.
I have seen inside the WK8 and KorgI30 and X1 and all 3 are totally unique, eg, the keys are fitted on a circuit board that has a specific cable with the plug being sized to fit that specific part of the circuitry. And then the keys themselves are cut to slot into some stabalised holes, for example on the X1 they are even screwed directly on the base of the keyboard casing (so they are visible to the eye).
So the answer to your question is NO unless its customised (very risky) or if there is a way I dont know of it.
Korg: Pa5x 61, Pa4x 76, Pa1000, Pa900, Pa800, Pa700RD, Pa600, Pa500 & i30
Ketron: Event 76 & SD60
Roland: BK9x2 & EA7
Yamaha: Genos, SX900, S-975, PSR9000
GEM: WK8 Megastation