I suspect TE wanted to outright replace the OP-1 with the OP-z, but the OP-z is not a direct replacement(?) and its initial marketing seemed to me to suggest it is/was going to be a very different device.
For the music hackers out there I'd recommend checking out the Critter and Guitari Organelle M as a more budget (<$500us) and FOSS friendly alternative. The new organelle M has a Raspberry PI compute module under the hood.