Just be aware that the outermost keys in the thumb cluster on the ErgoDox are not as accessible as on the Kinesis, because of it being in the same plane. Most flat DIY ergo-mech keyboards have the thumb cluster smaller and/or close to the fingers for that reason.
Of the keyboards I've saved images of, the only one satisfying your description was hand-wired, not a PCB, sorry. But I'm sure I've seen several like it somewhere sometime ...
Maltron has made flat versions of their contoured keyboard, but I dunno how to get one, and if you do, it will probably be expensive, and you might not appreciate how it was put together. (Maltrons are hand-wired on a plastiic plate...)
You could also take a look at the "Alice-like" keyboards but with columns, such has the Jabberwocky and Red Herring, but I don't think there are PCB design files available.