I know what you mean about most neckers, I think it just stems from the fact that most people won't be comfortable carrying neckers that are longer than 7" overall.

I know for a fact that a Scrapivore is about as much knife as I want hanging off my neck, anything more and I'd just have it riding on a belt.

Another thing I feel needs improving for neckers is rounded corners of the handle to make them more comfortable against your body. The Scrapivore really illustrates this point with the pry bar end, the last thing you want is sharp(ish) metal jabbing you in bony areas.