With this configuration a 4x12 jj40 (with 48 keys) is being removed 20 keys and transformed into an ortholinear Alpha28 PyroL-vderm 28 keys inspired layout one. This keyboard can be actually called jj28!
Why you should want to do something like this? There are many valid reasons. The main one to me might just be to be able to test such an "extreme" configuration for real if you have this easily available board on hand. But also because this setup might be even more confortable than the original 2u space one (for muscle memory having bnm letters nearer to zxcv). Or just more nice looking. Surely you have an additional option, and personally, after using it as a daily driver, I liked it, even if I was a bit slower in processing complicated sequences! :)
Notes on layout: After few tests I found out that the space at the end is the best for people that are very used to “standard” keyboards (basically almost everybody), retaining years of muscle memory. And moreover, also shift, fn and numsym layer keys are good to be replicated on central line.
Keyboard layout editor raw data in keyboard-layout-editor-raw-data.txt file.