Yes, Kepler proposed this model at first, but withdrew it when he discovered what we now call Kepler’s Laws, which state that planetary orbits are ellipses. I think we specifically can’t count a hypothesis here if the scientist in question abandons it in light of evidence. That’s how the scientific method works. This example is actually a particularly good parallel to string theory.
Nitpick: The bit about the length of objects changing wasn’t Einstein’s idea, it was proposed by Hendrik Lorentz and George Fitzgerald in 1904, a year before Einstein picked up the idea.
Kepler did, however, hang on to the notion of “The Music of The Spheres”, believing planetary motions to correspond to musical harmonies. He published “Harmonice Mundi” after having formulated the first two laws of planetary motion in “Astronomia nova” 10 years earlier, and presented the third in that work, intertwined with a bunch of Astrology:
Kepler remained a Pythagorian mystic and Astrologer. Astrology and Astronomy weren’t really clearly separated in his era. Kepler firmly believed that the motions of the heavens influenced human affairs, and he was trying to unravel exactly how it worked.