QMK is an open source community based on making human interface devices such as keyboards, mice and MIDI controllers. A brief video has been shared showing what looks very much like an OP-1 inspired keyboard controller, built using QMK - which now has support for step sequencers.
It's described as a tribute to the OP-1 and features multiple rotary encoders and lights for the music making version. The github page is in Japanese but can be translated here. It appears to be a later iteration of his Jones model - with some added encoders and a musical keyboard layout.
The QMK Sequencer has been shared by GitHub user 'jpskenn' which is available to view here.