So things we definitely won't see on Silk Road;
- contracts/bounties to commit true crime hits (including assassination contracts)
- property acquired through theft of any kind (including body parts, stolen bitcoins, etc)
- criminal activity involving victims (including child porn, slave trade, fraudulent schemes, etc)
Things we might see;
- legitimate trade in substances and content that may be otherwise illicit in some legal systems (pharmaceuticals, censored material, leaked explosive govt. documents)
- legitimate trade in radioactive isotopes (maybe there is a market for fringe clean-up around Fukushima)
- legitimate trade in weapons, explosives and other destructive technologies (bio-weapons, chemical weapons)
- trade in gene selection technology for designer offspring and other ethically-questionable, experimental bio-medical technologies, fringe cancer treatments, etc
.....
good summary or wide of the mark?
Well, it's speculation... the rules are all up to Silkroad, but here are my comments on your list...
There could be a legitimate reason for wanting an individual killed. Perhaps they are a member of the police or other authority and are threatening you or your family.
It's not always clear whether property is stolen or legitimate, and I think any system to discriminate between them should be voluntary. Silk Road is free to put in place such a system if they choose.
I'm not convinced that possessing or viewing child porn is immoral, only creating it with actual children.