Browsing the galleries of the 2nd Leipzig Meetup, I came across apfel's (aka kilipan) Zilpzalp:
A wonky 28-key, column-staggered, unibody-split keyboard made with fantastic FOSS software: ergogen and KiCad – kilipan.
Zilpzalp was inspired by Peter Elliot's Hummingbird keyboard, with a few changes for its author's personal convenience: thumb keys are "much more reachy" and splayed, and the pinky only has one key left with a significantly increased stagger.
There are four variants available:
default Choc spacing, solder only
Choc spacing with hotswap support (extra space required by the socket)
Minimal Choc, solder only – "with the tightest spacing that choc V1 switches allow" – no commercially available caps for this version, the author recommends Pseudoku's Philadelphia Minimalist.
CFX version (also known as "cfxilpcfxalp"), which is almost 1.5 cm smaller horizontally.