I've been working on this as a student project, and I'm at the point where it's looking pretty good to me, but I'm hoping someone with more experienced eyes can point out the flaws I'm missing.
I've done upper/lower/figures/punctuation and extended western European so far. Most are based on the specimen I managed to get a copy of, but I filled in a lot of missing characters myself, inspired by the various existing versions of Kabel. I haven't done any kerning yet, but the sidebearings are working reasonably well.
I'm also really curious whether anyone has even seen this design before. It's Rudolf Koch's swash capitals designed to pair with lowercase Kabel—it was never given its own name (Kabella is my name for the revival) and there seems to be very little information available about it. He really seemed to love mixing different styles of upper and lowercase. Koch was really a fascinating character (no pun intended).