It is official now:

arturia.com Arturia - Overview The sequencer the world has been waiting for. KeyStep Pro gives keyboard players incredible sequencing and performance power in a compact, versatile c...

It was anounced in a website, removed now. I could save some images. Rumored price 349€

Features :

4 polyphonic track, with up to 16 notes per step (via midi?)

All tracks can act as an arpegiator

Probability per step

Patter nudge via 2 dedicated buttons

Metronome via included speaker or audio out

16 projects, 16 pattern per track up to 64 steps

My keystep may need a new home soon…