Here is how i think it should be done:
You create a Blockchain Application/program that can verify any valuable asset on the Blockchain and link it to owner's Virtual ID Card WITHOUT THE SLIGHTEST POSSIBILITY of knowing who the owner is . The asset can be anything from Anonymous Websites, Cryptocurrencies(ones with good anonymity), softwares, Virtual gold etc assets without great anonymity will not be accepted. It should be completely anonymous, transparent & legal assets(Guess illegal assets would be ones that violate or could violate people's fundamental rights) .
The asset will be linked to the owners Virtual identify CARD which can be used as trust, collateral or verification purposes anywhere on the Blockchain. The I'd card will be 100% hack proof, very anonymous with great privacy. The ID card would be great on Ethereum network.
There are requirements here that would entail some measure of trade-off. For example, you would need some form of identity although you could get by with a pseudonymous identifier for most tasks.
The Anonymous ID Card idea could help pretect people from the hugh number of scammers on cryptocurrency. Could also help compliment Escrow service.
The example you gave with an artist commissioned to do design work is difficult more so because either party's definition of "done" could be in disagreement. So you would have to consider what courses of action are reasonable in case either party is unsatisfied with a completed service (which would depend very much on the use case.) However, there should be no problem enforcing the prior agreements defined in a Smart Contract.